drm/i915: Simplify internal helper function signature

Since we are now storing the GT backpointer in the wa list we can drop the
explicit struct intel_gt * argument to wa_list_apply.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Andrzej Hajda <andrzej.hajda@intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221110124633.3135026-1-tvrtko.ursulin@linux.intel.com