media: v4l: omap_vout: vrfb: remove an unused variable

We now get a warning after the 'dmadev' variable is no longer used:

drivers/media/platform/omap/omap_vout_vrfb.c: In function 'omap_vout_prepare_vrfb':
drivers/media/platform/omap/omap_vout_vrfb.c:239:21: error: unused variable 'dmadev' [-Werror=unused-variable]

Fixes: 8f0aa382 ("media: v4l: omap_vout: vrfb: Use the wrapper for prep_interleaved_dma()")

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>