staging: gdm72xx: fix leaks at failure path in gdm_usb_probe()

Error handling code in gdm_usb_probe() misses to deallocate
tx_ and rx_structs and to do usb_put_dev().

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

Signed-off-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>