drm/i915: Make intel_plane_restore() return an error

Propagate the error from intel_update_plane() up through
intel_plane_restore() to the caller. This will be used for
rollback purposes when setting properties fails.

Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>