cmd_usb_mass_storage: Use 'USB Mass Storage' in the help text

USB Mass Storage is the standard name, so let's use it here.

Suggested-by: Soeren Moch <smoch@web.de>
Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Acked-by: Marek Vasut <marex@denx.de>

common/cmd_usb_mass_storage.c

@@ -159,7 +159,7 @@ exit:
 }
 
 U_BOOT_CMD(ums, 4, 1, do_usb_mass_storage,
-	"Use the UMS [User Mass Storage]",
+	"Use the UMS [USB Mass Storage]",
 	"<USB_controller> [<devtype>] <devnum>  e.g. ums 0 mmc 0\n"
 	"    devtype defaults to mmc"
 );