Fix ltfs -o device_list exit code (#429)

Author: diamant3

src/libltfs/ltfs.c

@@ -4371,7 +4371,7 @@ int ltfs_print_device_list(struct tape_ops *ops)
 		}
 	}
 
-	ret = 0;
+	//ret = 0;
 
 	return ret;
 }

src/main.c

@@ -708,7 +708,7 @@ int main(int argc, char **argv)
 	if (priv->device_list) {
 		ret = show_device_list(priv);
 		ltfs_finish();
-		return (ret != 0) ? 0 : 1;
+		return ret ? 1 : 0;
 	}
 
 	/* Validate sync option */