drm/xe: Use ARRAY_SIZE in guc_waklv_init()

Prefer using ARRAY_SIZE where needed and just passing 1 instead of
calculating the size of one element.

Cc: Jonathan Cavitt <jonathan.cavitt@intel.com>
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202508130158.eogeBZQT-lkp@intel.com/


Reviewed-by: Jonathan Cavitt <jonathan.cavitt@intel.com>
Link: https://lore.kernel.org/r/20250912-guc-ads-array-size-v1-1-a6555392a1f8@intel.com


Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>