drm/xe: remove unused LE_COS

drm/xe: remove unused LE_COS

The LE_COS definition missed passing the value parameter to
REG_FIELD_PREP. This didn't cause build errors because the entire
macro was unused.
The value for this field is universally "0" for every MOCS entry on
the old Xe_LP platforms, and the whole field has been removed from
Xe_HP onward. Just delete the line so that we don't have an unused
definition.

Suggested-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Signed-off-by: Shuicheng Lin <shuicheng.lin@intel.com>
Link: https://lore.kernel.org/r/20250405171539.599850-1-shuicheng.lin@intel.com
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>