media: v4l: omap_vout: vrfb: include linux/slab.h

Without this header, we get a build error in some configurations:

drivers/media/platform/omap/omap_vout_vrfb.c: In function 'omap_vout_setup_vrfb_bufs':
drivers/media/platform/omap/omap_vout_vrfb.c:143:26: error: implicit declaration of function 'kzalloc'; did you mean 'vzalloc'? [-Werror=implicit-function-declaration]

Fixes: 6a1560ec ("media: v4l: omap_vout: vrfb: Convert to dmaengine")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

drivers/media/platform/omap/omap_vout_vrfb.c

@@ -12,6 +12,7 @@
 #include <linux/sched.h>
 #include <linux/platform_device.h>
 #include <linux/videodev2.h>
+#include <linux/slab.h>
 
 #include <media/videobuf-dma-contig.h>
 #include <media/v4l2-device.h>