media: davinci: vpif_capture: fix potential NULL deref

Fix potential NULL pointer dereference in the error path of memory
allocation failure.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>