[media] radio-si470x: fix memory leak in si470x_usb_driver_probe()

radio->int_in_urb is not deallocated on error paths in si470x_usb_driver_probe().

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

Signed-off-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>