net: macb: fix an issue about leak related system resources

A call of the function macb_init() can fail in the function
fu540_c000_init. The related system resources were not released
then. use devm_platform_ioremap_resource() to replace ioremap()
to fix it.

Fixes: c218ad55 ("macb: Add support for SiFive FU540-C000")
Cc: Andy Shevchenko <andy.shevchenko@gmail.com>
Reviewed-by: Yash Shah <yash.shah@sifive.com>
Suggested-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Suggested-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Dejin Zheng <zhengdejin5@gmail.com>
Acked-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Signed-off-by: David S. Miller <davem@davemloft.net>