usb: gadget: uvc: drop vb2_ops_wait_prepare/finish

Since commit 88785982 ("media: vb2: use lock if wait_prepare/finish
are NULL") it is no longer needed to set the wait_prepare/finish
vb2_ops callbacks as long as the lock field in vb2_queue is set.

Since the vb2_ops_wait_prepare/finish callbacks already rely on that field,
we can safely drop these callbacks.

This simplifies the code and this is a step towards the goal of deleting
these callbacks.

Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: linux-usb@vger.kernel.org
Link: https://lore.kernel.org/r/2fb746b8-31c4-44e0-bf7b-7a0758edf52a@xs4all.nl


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>