media: v4l: omap_vout: vrfb: initialize DMA flags

Passing uninitialized flags into device_prep_interleaved_dma is clearly
a bad idea, and we get a compiler warning for it:

drivers/media/platform/omap/omap_vout_vrfb.c: In function 'omap_vout_prepare_vrfb':
drivers/media/platform/omap/omap_vout_vrfb.c:273:5: error: 'flags' may be used uninitialized in this function [-Werror=maybe-uninitialized]

It seems that the OMAP dmaengine ignores the flags, but we should
pick the right ones anyway. This sets the flags I guessed based
on what other drivers used, and Peter confirmed that they are the
right ones.

Fixes: 6a1560ec ("media: v4l: omap_vout: vrfb: Convert to dmaengine")

Acked-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
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>