net: stmmac: platform: convert to devm_platform_ioremap_resource

Use devm_platform_ioremap_resource() to simplify code, which
contains platform_get_resource and devm_ioremap_resource.

Signed-off-by: Dejin Zheng <zhengdejin5@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>