media: radio-si476x: Unregister v4l2_device on probe failure

In the Linux kernel, the following vulnerability has been resolved: media: radio-si476x: Unregister v4l2_device on probe failure si476x_radio_probe() registers radio->v4l2dev before allocating the V4L2 controls and before registering the video device. If any of those later steps fails, probe returns through the exit label after freeing only the control handler. A failed probe does not call si476x_radio_remove(), so the v4l2_device_unregister() there is not reached. This leaves the parent device reference taken by v4l2_device_register() behind on the error path. Unregister the V4L2 device in the probe error path after freeing the controls.