disk: Return the partition number in part_get_info_by_name()

Similar to what blk_get_device_part_str() does, this patch makes
part_get_info_by_name() return the partition number in case of a match.
This is useful when the partition number is needed and not just the
descriptor.

Signed-off-by: Alex Deymo <deymo@google.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

disk/part.c

@@ -635,7 +635,7 @@ int part_get_info_by_name(struct blk_desc *dev_desc, const char *name,
 			}
 			if (strcmp(name, (const char *)info->name) == 0) {
 				/* matched */
-				return 0;
+				return i;
 			}
 		}
 	}