[media] lirc_imon: do not leave imon_probe() with mutex held

Commit af8a819a ("[media] lirc_imon: simplify error handling code")
lost mutex_unlock(&context->ctx_lock), so imon_probe() exits with
the context->ctx_lock mutex acquired.

The patch adds mutex_unlock(&context->ctx_lock) back.

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

Fixes: af8a819a ("[media] lirc_imon: simplify error handling code")
Signed-off-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>

drivers/staging/media/lirc/lirc_imon.c

@@ -885,12 +885,14 @@ static int imon_probe(struct usb_interface *interface,
 		vendor, product, ifnum, usbdev->bus->busnum, usbdev->devnum);
 
 	/* Everything went fine. Just unlock and return retval (with is 0) */
+	mutex_unlock(&context->ctx_lock);
 	goto driver_unlock;
 
 unregister_lirc:
 	lirc_unregister_driver(driver->minor);
 
 free_tx_urb:
+	mutex_unlock(&context->ctx_lock);
 	usb_free_urb(tx_urb);
 
 free_rx_urb: