usb: gadget: goku_udc: fix memory leak in goku_probe()

Memory allocated for goku_udc device is not deallocated at error
paths in goku_probe(), because gadget_release() destructor
is not registered yet.

Found by Linux Driver Verification project (linuxtesting.org).

Signed-off-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>