drm/vc4: Revert part of earlier commit

Commit "bbfbe89 drm/vc4: Add support for DRM_FORMAT_P030 to vc4 planes"
inadvertently included a logic fix that has now been fixed upstream.
Revert that fix to allow for the upstream one.

(Ideally this should be squashed into "drm/vc4: Add support for DRM_FORMAT_P030
to vc4 planes")

Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>

drivers/gpu/drm/vc4/vc4_plane.c

@@ -965,8 +965,8 @@ static int vc4_plane_mode_set(struct drm_plane *plane,
 		vc4_dlist_write(vc4_state,
 				VC4_SET_FIELD(state->alpha >> 4,
 					      SCALER5_CTL2_ALPHA) |
-				(fb->format->has_alpha ?
-					SCALER5_CTL2_ALPHA_PREMULT : 0) |
+				fb->format->has_alpha ?
+					SCALER5_CTL2_ALPHA_PREMULT : 0 |
 				(mix_plane_alpha ?
 					SCALER5_CTL2_ALPHA_MIX : 0) |
 				VC4_SET_FIELD(fb->format->has_alpha ?