libceph: simplify ceph_monc_handle_map()

ceph_monc_handle_map() confuses static checkers which report a
false use-after-free on monc->monmap, missing that monc->monmap and
client->monc.monmap is the same pointer.

Use monc->monmap consistently and get rid of "old", which is redundant.
Signed-off-by: NIlya Dryomov <idryomov@gmail.com>

net/ceph/mon_client.c

@@ -467,7 +467,7 @@ static void ceph_monc_handle_map(struct ceph_mon_client *monc,
 				 struct ceph_msg *msg)
 {
 	struct ceph_client *client = monc->client;
-	struct ceph_monmap *monmap = NULL, *old = monc->monmap;
+	struct ceph_monmap *monmap;
 	void *p, *end;
 
 	mutex_lock(&monc->mutex);
@@ -484,13 +484,13 @@ static void ceph_monc_handle_map(struct ceph_mon_client *monc,
 		goto out;
 	}
 
-	if (ceph_check_fsid(monc->client, &monmap->fsid) < 0) {
+	if (ceph_check_fsid(client, &monmap->fsid) < 0) {
 		kfree(monmap);
 		goto out;
 	}
 
-	client->monc.monmap = monmap;
-	kfree(old);
+	kfree(monc->monmap);
+	monc->monmap = monmap;
 
 	__ceph_monc_got_map(monc, CEPH_SUB_MONMAP, monc->monmap->epoch);
 	client->have_fsid = true;