can: esd_usb2: fix memory leak on disconnect

It seems struct esd_usb2 dev is not deallocated on disconnect. The patch adds
the missing deallocation.

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

Signed-off-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
Acked-by: Matthias Fuchs <matthias.fuchs@esd.eu>
Cc: linux-stable <stable@vger.kernel.org>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
diff --git a/drivers/net/can/usb/esd_usb2.c b/drivers/net/can/usb/esd_usb2.c
index b7c9e8b..7a90075 100644
--- a/drivers/net/can/usb/esd_usb2.c
+++ b/drivers/net/can/usb/esd_usb2.c
@@ -1143,6 +1143,7 @@
 			}
 		}
 		unlink_all_urbs(dev);
+		kfree(dev);
 	}
 }