fs/locks: always delete_block after waiting.

Now that requests can block other requests, we
need to be careful to always clean up those blocked
requests.
Any time that we wait for a request, we might have
other requests attached, and when we stop waiting,
we must clean them up.
If the lock was granted, the requests might have been
moved to the new lock, though when merged with a
pre-exiting lock, this might not happen.
In all cases we don't want blocked locks to remain
attached, so we remove them to be safe.

Signed-off-by: NeilBrown <neilb@suse.com>
Reviewed-by: J. Bruce Fields <bfields@redhat.com>
Tested-by:  <syzbot+a4a3d526b4157113ec6a@syzkaller.appspotmail.com>
Tested-by: kernel test robot <rong.a.chen@intel.com>
Signed-off-by: Jeff Layton <jlayton@kernel.org>