drm/omap: Follow implicit fencing in prepare_fb

I guess no one ever tried running omap together with lima or panfrost,
not even sure that's possible. Anyway for consistency, fix this.
Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Tomi Valkeinen <tomba@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20210622165511.3169559-12-daniel.vetter@ffwll.ch

drivers/gpu/drm/omapdrm/omap_plane.c

@@ -6,6 +6,7 @@
 
 #include <drm/drm_atomic.h>
 #include <drm/drm_atomic_helper.h>
+#include <drm/drm_gem_atomic_helper.h>
 #include <drm/drm_plane_helper.h>
 
 #include "omap_dmm_tiler.h"
@@ -29,6 +30,8 @@ static int omap_plane_prepare_fb(struct drm_plane *plane,
 	if (!new_state->fb)
 		return 0;
 
+	drm_gem_plane_helper_prepare_fb(plane, new_state);
+
 	return omap_framebuffer_pin(new_state->fb);
 }