fuse: Fetch a queued fuse request on command registration

With the reduced queue feature io-uring is marked as ready after
receiving the 1st ring entry. At this time other queues just
might be in the process of registration and then a race happens

fuse_uring_queue_fuse_req -> no queue entry registered yet
    list_add_tail -> fuse request gets queues

So far fetching requests from the list only happened from
FUSE_IO_URING_CMD_COMMIT_AND_FETCH, but without new requests
on the same queue, it would actually never send requests
from that queue - the request was stuck.

Author: bsbernd

fs/fuse/dev_uring.c

@@ -1379,6 +1379,8 @@ static int fuse_uring_register(struct io_uring_cmd *cmd,
 
 	fuse_uring_do_register(ent, cmd, issue_flags);
 
+	fuse_uring_next_fuse_req(ent, queue, issue_flags);
+
 	return 0;
 }