part: call part_init() in blk_get_device_by_str() only for MMC

In blk_get_device_by_str(), the comment says: "Updates the partition table
for the specified hw partition."
Since hw partition is supported only on MMC, it makes no sense to do so
for other devices.

Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
Reviewed-by: Simon Glass <sjg@chromium.org>

disk/part.c

@@ -430,7 +430,8 @@ int blk_get_device_by_str(const char *ifname, const char *dev_hwpart_str,
 	 * Always should be done, otherwise hw partition 0 will return stale
 	 * data after displaying a non-zero hw partition.
 	 */
-	part_init(*dev_desc);
+	if ((*dev_desc)->if_type == IF_TYPE_MMC)
+		part_init(*dev_desc);
 #endif
 
 cleanup: