Fix the devmtx lock leak from make_dev(9) when the old device cloning

failed due to invalid or duplicated path being generated.

Reviewed by:	jh
Approved by:	re (kensmith)
MFC after:	1 week

sys/kern/kern_conf.c

@@ -764,7 +764,8 @@ make_dev_credv(int flags, struct cdev **dres, struct cdevsw *devsw, int unit,
 				LIST_REMOVE(dev, si_list);
 				dev_unlock();
 				devfs_free(dev);
-			}
+			} else
+				dev_unlock();
 			return (res);
 		}
 	}