libceph: kill ceph_osdc_create_event() "one_shot" parameter

There is only one caller of ceph_osdc_create_event(), and it
provides 0 as its "one_shot" argument.  Get rid of that argument and
just use 0 in its place.

Replace the code in handle_watch_notify() that executes if one_shot
is nonzero in the event with a BUG_ON() call.

While modifying "osd_client.c", give handle_watch_notify() static
scope.

Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>

drivers/block/rbd.c

@@ -1744,7 +1744,7 @@ static int rbd_dev_header_watch_sync(struct rbd_device *rbd_dev, int start)
 	rbd_assert(start ^ !!rbd_dev->watch_request);
 
 	if (start) {
-		ret = ceph_osdc_create_event(osdc, rbd_watch_cb, 0, rbd_dev,
+		ret = ceph_osdc_create_event(osdc, rbd_watch_cb, rbd_dev,
 						&rbd_dev->watch_event);
 		if (ret < 0)
 			return ret;