drm/i915/skl: Replace BUG() by MISSING_CASE() in skl_plane_ctl_format()

Let's be consistent with the others skl_plane_ctl_*() functions and use
a MISSING_CASE(). Not only that, but it's a rude to BUG() the whole
machine here.
Signed-off-by: NDamien Lespiau <damien.lespiau@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_display.c

@@ -2997,7 +2997,7 @@ u32 skl_plane_ctl_format(uint32_t pixel_format)
 		format = PLANE_CTL_FORMAT_YUV422 | PLANE_CTL_YUV422_VYUY;
 		break;
 	default:
-		BUG();
+		MISSING_CASE(pixel_format);
 	}
 
 	return format;