[media] v4l: xilinx: missing error code

We should set "ret" on this error path instead of returning success.

Fixes: df330515 ('[media] v4l: xilinx: Add Xilinx Video IP core')

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Hyun Kwon <hyun.kwon@xilinx.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>