net: fsl_pq_mdio: use platform_{get,set}_drvdata()

Use the wrapper functions for getting and setting the driver data using
platform_device instead of using dev_{get,set}_drvdata() with &pdev->dev,
so we can directly pass a struct platform_device.

Signed-off-by: Libo Chen <libo.chen@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>