drm/i915/hwmon: Fix a build error used with clang compiler

drm/i915/hwmon: Fix a build error used with clang compiler

Use REG_FIELD_PREP() and a constant value for hwm_field_scale_and_write()

If the first argument of FIELD_PREP() is not a compile-time constant value
or unsigned long long type, this routine of the __BF_FIELD_CHECK() macro
used internally by the FIELD_PREP() macro always returns false.

 BUILD_BUG_ON_MSG(__bf_cast_unsigned(_mask, _mask) >      \
                  __bf_cast_unsigned(_reg, ~0ull),        \
                  _pfx "type of reg too small for mask"); \

And it returns a build error by the option among the clang
compilation options. [-Werror,-Wtautological-constant-out-of-range-compare]

Reported build error while using clang compiler:

drivers/gpu/drm/i915/i915_hwmon.c:115:16: error: result of comparison of
constant 18446744073709551615 with expression of type 'typeof (_Generic((field_msk),
char: (unsigned char)0, unsigned char: (unsigned char)0, signed char: (unsigned char)0,
unsigned short: (unsigned short)0, short: (unsigned short)0, unsigned int:
(unsigned int)0, int: (unsigned int)0, unsigned long: (unsigned long)0, long:
(unsigned long)0, unsigned long long: (unsigned long long)0, long long:
(unsigned long long)0, default: (field_msk)))' (aka 'unsigned int') is always false
[-Werror,-Wtautological-constant-out-of-range-compare]
        bits_to_set = FIELD_PREP(field_msk, nval);
                      ^~~~~~~~~~~~~~~~~~~~~~~~~~~
./include/linux/bitfield.h:114:3: note: expanded from macro 'FIELD_PREP'
                __BF_FIELD_CHECK(_mask, 0ULL, _val, "FIELD_PREP: ");    \
                ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
./include/linux/bitfield.h:71:53: note: expanded from macro '__BF_FIELD_CHECK'
                BUILD_BUG_ON_MSG(__bf_cast_unsigned(_mask, _mask) >     \
                ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~
./include/linux/build_bug.h:39:58: note: expanded from macro 'BUILD_BUG_ON_MSG'
                                    ~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~
./include/linux/compiler_types.h:357:22: note: expanded from macro 'compiletime_assert'
        _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
        ~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
./include/linux/compiler_types.h:345:23: note: expanded from macro '_compiletime_assert'
        __compiletime_assert(condition, msg, prefix, suffix)
        ~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
./include/linux/compiler_types.h:337:9: note: expanded from macro '__compiletime_assert'
                if (!(condition))                                       \

v2: Use REG_FIELD_PREP() macro instead of FIELD_PREP() (Jani)

Fixes: 99f55efb7911 ("drm/i915/hwmon: Power PL1 limit and TDP setting")
Cc: Ashutosh Dixit <ashutosh.dixit@intel.com>
Cc: Anshuman Gupta <anshuman.gupta@intel.com>
Cc: Andi Shyti <andi.shyti@linux.intel.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Gwan-gyeong Mun <gwan-gyeong.mun@intel.com>
Reviewed-by: Ashutosh Dixit <ashutosh.dixit@intel.com>
Acked-by: Jani Nikula <jani.nikula@intel.com>
[Joonas: Wrapped commit message error line length to be more reasonable]
Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221029044230.32128-1-gwan-gyeong.mun@intel.com