media: rcar_drif: fix error return code in rcar_drif_alloc_dmachannels()

Fix to return error code -ENODEV from the dma_request_slave_channel()
error handling case instead of 0, as done elsewhere in this function.
rc can be overwrite to 0 by dmaengine_slave_config() in the for loop.

Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Ramesh Shanmugasundaram <Ramesh.shanmugasundaram@bp.renesas.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>