cmd: usb_mass_storage: Use part_get_info_by_dev_and_name_or_num

This allows specifying partitions using more extended syntax. This is
particularly useful to access eMMC hardware partitions. For example,
this allows something like

	ums 0 mmc 0.0,0.1,0.2,0.3

to expose four LUNs for each of the four default eMMC hardware
partitions. Note that the comma syntax was already present, and this
syntax is already documented.

Signed-off-by: Sean Anderson <sean.anderson@seco.com>
diff --git a/cmd/usb_mass_storage.c b/cmd/usb_mass_storage.c
index 14fa723..d4e619b 100644
--- a/cmd/usb_mass_storage.c
+++ b/cmd/usb_mass_storage.c
@@ -74,8 +74,8 @@
 		if (!devnum_part_str)
 			break;
 
-		partnum = blk_get_device_part_str(devtype, devnum_part_str,
-					&block_dev, &info, 1);
+		partnum = part_get_info_by_dev_and_name_or_num(devtype, devnum_part_str,
+							       &block_dev, &info, 1);
 
 		if (partnum < 0)
 			goto cleanup;