[media] v4l: vb2: Fix race condition in _vb2_fop_release
The function releases the queue if the file being released is the queue
owner. The check reads the queue->owner field without taking the queue
lock, creating a race condition with functions that set the queue owner,
such as vb2_ioctl_reqbufs() for instance.
Fix this by moving the queue->owner check within the mutex protected
section.