media: saa7146: fix error return from master_xfer

Returning -1 (-EPERM) is not appropriate here, go with -EIO.

Signed-off-by: Peter Rosin <peda@axentia.se>
Signed-off-by: Hans Verkuil <hansverk@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>