9p: return NULL when trans not found

v9fs_match_trans function returns arbitrary transport module instead of NULL
when the requested transport is not registered. This patch modifies the
function to return NULL in that case.
Signed-off-by: Latchesar Ionkov <lucho@ionkov.net>
Acked-by: Eric Van Hensbergen <ericvh@gmail.com>

net/9p/mod.c

@@ -76,9 +76,9 @@ struct p9_trans_module *v9fs_match_trans(const substring_t *name)
 	list_for_each(p, &v9fs_trans_list) {
 		t = list_entry(p, struct p9_trans_module, list);
 		if (strncmp(t->name, name->from, name->to-name->from) == 0)
-			break;
+			return t;
 	}
-	return t;
+	return NULL;
 }
 EXPORT_SYMBOL(v9fs_match_trans);