[media] saa7164: better handle error codes

Right now, the driver is doing the right thing for
PVC_ERRORCODE_UNKNOWN and PVC_ERRORCODE_INVALID_CONTROL:
for both, it returns an error code (SAA_ERR_NOT_SUPPORTED).

However, it is printing two error messages instead of one
on those cases.

Fix the logic.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>