userns: On mips modify check_same_owner to use uid_eq

userns: On mips modify check_same_owner to use uid_eq

The kbuild test robot <fengguang.wu@intel.com> report the following error
when building mips with user namespace support enabled.

All error/warnings:
arch/mips/kernel/mips-mt-fpaff.c: In function 'check_same_owner':
arch/mips/kernel/mips-mt-fpaff.c:53:22: error: invalid operands to binary == (have 'kuid_t' and 'kuid_t')
arch/mips/kernel/mips-mt-fpaff.c:54:15: error: invalid operands to binary == (have 'kuid_t' and 'kuid_t')

Replace "a == b" with uid_eq(a, b) removes this error and allows the
code to work with user namespaces enabled.

Cc: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>