[media] vb2: fix wrong owner check

Check against q->fileio to see if the queue owner should be set or not.
The former check against the return value of read or write is wrong, since
read/write can return an error, even if the queue is in streaming mode.
For example, EAGAIN when in non-blocking mode.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>