MIPS: pci-mt7620: Use devm_platform_get_and_ioremap_resource()

Convert platform_get_resource(), devm_ioremap_resource() to a single
call to devm_platform_get_and_ioremap_resource(), as this is exactly
what this function does.

Signed-off-by: Ye Xingchen <ye.xingchen@zte.com.cn>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>