[media] saa7164: saa7164_vbi_stop_port() returns linux error codes

The saa7164_vbi_stop_port() changes the SAA_ERR_ALREADY_STOPPED result
code to -EIO before returning.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>