libusbg: Fix usbg_disable_gadget to actually clear the UDC
libusbg: Fix usbg_disable_gadget to actually clear the UDC

Currently usbg_disable_gadget() does not actually write anything
to UDC to clear it and the configured UDC name stays there.

Signed-off-by: Tony Lindgren <1001e8702733cced254345e193c88aaa47a4f5de@atomide.com>
Reviewed-by: Krzysztof Opasiak <8064eda6f94b3817252b7d7649cf754592f63500@samsung.com>

pszewczyk/libusbg,pszewczyk/libusbg