ovl: print error message for invalid mount options

Overlayfs should print an error message if an incorrect mount option
is caught like other filesystems.

After this patch, improper option input could be clearly known.
Reported-by: NFabian Sturm <fabian.sturm@aduu.de>
Signed-off-by: Nhujianyang <hujianyang@huawei.com>
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>

fs/overlayfs/super.c

@@ -615,6 +615,7 @@ static int ovl_parse_opt(char *opt, struct ovl_config *config)
 			break;
 
 		default:
+			pr_err("overlayfs: unrecognized mount option \"%s\" or missing value\n", p);
 			return -EINVAL;
 		}
 	}