Use mass_storage also as fake charging mode with android gadget

Seems an empty android gadget only enumerates if some configuration had
been used before. Fix this by using mass_storage to make a similar fake
mass_storage device as used with normal modules.

[usb-moded] Use fake mass_storage for android gadget charging mode. Fixes: JB#8277

Signed-off-by: Philippe De Swert <philippe.deswert@jollamobile.com>