drm/i915/overlay: Fix active retire callback alignment

__i915_active_call annotation is required on the retire callback to ensure
correct function alignment.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Fixes: a21ce8ad ("drm/i915/overlay: Switch to using i915_active tracking")
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Matthew Auld <matthew.auld@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210429083530.849546-1-tvrtko.ursulin@linux.intel.com