drm/omap: add missing seq_file include

This fails to build with missing seq declerations.

Fixes: 9e2b84f ("drm/print: drop include seq_file.h")
Signed-off-by: Dave Airlie <airlied@redhat.com>

Author: airlied

drivers/gpu/drm/omapdrm/omap_fb.c

@@ -5,6 +5,7 @@
  */
 
 #include <linux/dma-mapping.h>
+#include <linux/seq_file.h>
 
 #include <drm/drm_blend.h>
 #include <drm/drm_modeset_helper.h>