drm/i915/huc: use const struct bus_type pointers

drm/i915/huc: use const struct bus_type pointers

The struct bus_type pointers in the functions
intel_huc_register_gsc_notifier() and
intel_huc_unregister_gsc_notifier() should be a const pointer, as the
structure is not modified anywhere in the functions, and the pointer
they are passed will be a const * in the near future.

Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: David Airlie <airlied@gmail.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Alan Previn <alan.previn.teres.alexis@intel.com>
Cc: John Harrison <John.C.Harrison@Intel.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Tony Ye <tony.ye@intel.com>
Cc: Vitaly Lubart <vitaly.lubart@intel.com>
Cc: intel-gfx@lists.freedesktop.org
Cc: dri-devel@lists.freedesktop.org
Acked-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://lore.kernel.org/r/20230313182918.1312597-30-gregkh@linuxfoundation.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>