net: pcs-rzn1-miic: fix return value check in miic_probe()

net: pcs-rzn1-miic: fix return value check in miic_probe()

On failure, devm_platform_ioremap_resource() returns a ERR_PTR() value
and not NULL. Fix return value checking by using IS_ERR() and return
PTR_ERR() as error value.

Fixes: d2909d765ef7 ("net: pcs: add Renesas MII converter driver")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Reviewed-by: Clément Léger <clement.leger@bootlin.com>
Link: https://lore.kernel.org/r/20220628131259.3109124-1-yangyingliang@huawei.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>