videobuf2 has long been subject to AB-BA style deadlocks due to the
queue lock and mmap_sem being taken in different orders for the mmap and
get_unmapped_area operations. The problem has been fixed by making those
two operations callable without taking the queue lock, using an
mmap_lock internal to videobuf2.

The uvcvideo driver still calls the mmap and get_unmapped_area
operations with the queue lock held, resulting in a potential deadlock.
As the operations can now be called without locking the queue, fix it.
Reported-by: NBjørn Mork <bjorn@mork.no>
Signed-off-by: NLaurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: NMauro Carvalho Chehab <mchehab@osg.samsung.com>