phy: mdio-bcm-iproc: use devm_platform_ioremap_resource() to simplify code

Use devm_platform_ioremap_resource() to simplify the code a bit.
This is detected by coccinelle.

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Reviewed-by: Ray Jui <ray.jui@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>