disk: get_device_and_partition() return value fixes

When no valid partitions are found, guarantee that we return -1. This
most likely already happens, since the most recent get_partition_info()
will have returned an error. However, it's best to be explicit.

Remove an unnecessary assignment of ret=0 in the success case; this value
is over-written with the processed partition ID later.

Signed-off-by: Stephen Warren <swarren@nvidia.com>

disk/part.c

@@ -624,9 +624,9 @@ int get_device_and_partition(const char *ifname, const char *dev_part_str,
 			 */
 			if (p == MAX_SEARCH_PARTITIONS + 1)
 				*info = tmpinfo;
-			ret = 0;
 		} else {
 			printf("** No valid partitions found **\n");
+			ret = -1;
 			goto cleanup;
 		}
 	}