r128_drm.h: include drm/drm.h

Fixes compile error:

drm/r128_drm.h:156:23: error: array type has incomplete element type
  struct drm_clip_rect boxes[R128_NR_SAREA_CLIPRECTS];

Signed-off-by: Mikko Rapeli <mikko.rapeli@iki.fi>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

include/uapi/drm/r128_drm.h

@@ -33,6 +33,8 @@
 #ifndef __R128_DRM_H__
 #define __R128_DRM_H__
 
+#include <drm/drm.h>
+
 /* WARNING: If you change any of these defines, make sure to change the
  * defines in the X server file (r128_sarea.h)
  */