[media] omap_vout: Fix compile error in 3.1

This patch is against the mainline v3.1 release (c3b92c87) and
fixes a compile error when building for OMAP3+DSS+VOUT

Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Gary Thomas <gary@mlbassoc.com>
Cc: stable@kernel.org
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/video/omap/omap_vout.c

@@ -38,6 +38,7 @@
 #include <linux/irq.h>
 #include <linux/videodev2.h>
 #include <linux/dma-mapping.h>
+#include <linux/slab.h>
 
 #include <media/videobuf-dma-contig.h>
 #include <media/v4l2-device.h>