io_uring/msg_ring: move double lock/unlock helpers higher up

Commit 423d5081

 upstream.

In preparation for needing them somewhere else, move them and get rid of
the unused 'issue_flags' for the unlock side.

No functional changes in this patch.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>