bootstd: USB devtype detection for script boot

Change the device type from "usb_mass_storage" to "usb" when
booting a script.

Before this change:
   => printenv devtype
   devtype=usb_mass_storage

After this change:
   => printenv devtype
   devtype=usb

Signed-off-by: John Clark <inindev@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
1 file changed