media: vb2: set owner before calling vb2_read

Before vb2_read is called, the owner must be set since vb2_read will
actually start streaming. If vb2_read returns an error and q->fileio is
NULL, then it failed to start streaming and the owner is set back to NULL.

When the vb2 start_streaming callback is called, it expects the owner
pointer to be set, and that wasn't the case in this particular situation.

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>