9p/trans_fd: put worker reqs on destroy

p9_read_work/p9_write_work might still hold references to a req after
having been cancelled; make sure we put any of these to avoid potential
request leak on disconnect.

Fixes: 728356dedeff8 ("9p: Add refcount to p9_req_t")
Link: http://lkml.kernel.org/r/1539057956-23741-2-git-send-email-asmadeus@codewreck.org
Signed-off-by: Dominique Martinet <dominique.martinet@cea.fr>
Cc: Eric Van Hensbergen <ericvh@gmail.com>
Cc: Latchesar Ionkov <lucho@ionkov.net>
Reviewed-by: Tomas Bortoli <tomasbortoli@gmail.com>

net/9p/trans_fd.c

@@ -876,7 +876,15 @@ static void p9_conn_destroy(struct p9_conn *m)
 
 	p9_mux_poll_stop(m);
 	cancel_work_sync(&m->rq);
+	if (m->rreq) {
+		p9_req_put(m->rreq);
+		m->rreq = NULL;
+	}
 	cancel_work_sync(&m->wq);
+	if (m->wreq) {
+		p9_req_put(m->wreq);
+		m->wreq = NULL;
+	}
 
 	p9_conn_cancel(m, -ECONNRESET);