usb: ums: Kconfig: Select USB_FUNCTION_MASS_STORAGE when enabling 'ums' command

The CONFIG_USB_FUNCTION_MASS_STORAGE must be selected when one enables
support for ums command.

Signed-off-by: Lukasz Majewski <lukma@denx.de>
Reviewed-by: Jaehoon Chung <jh80.chung@samsung.com>
diff --git a/cmd/Kconfig b/cmd/Kconfig
index 676011d..051c1b6 100644
--- a/cmd/Kconfig
+++ b/cmd/Kconfig
@@ -929,6 +929,7 @@
 
 config CMD_USB_MASS_STORAGE
 	bool "UMS usb mass storage"
+	select USB_FUNCTION_MASS_STORAGE
 	help
 	  USB mass storage support