libusbg: Fix gadget-acm-ecm example to cleanup at exit.
libusbg: Fix gadget-acm-ecm example to cleanup at exit.

Make use of previously unused variable ret to cleanup
after successful gadget creation.

Signed-off-by: Krzysztof Opasiak <8064eda6f94b3817252b7d7649cf754592f63500@samsung.com>

pszewczyk/libusbg,pszewczyk/libusbg