uboot-imx

net: macb: Add remove callback

To avoid the failure of mdio_register(), add the remove callback
to unregister the mii_dev when removing the ethernet device.

Signed-off-by: Wenyou Yang <wenyou.yang@atmel.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>
Fixed up unused variable warning, e.g. for gurnard:
Signed-off-by: Simon Glass <sjg@chromium.org>