net: qcom/emac: fix return value check in emac_sgmii_config()

In case of error, the function ioremap() returns NULL pointer
not ERR_PTR(). The IS_ERR() test in the return value check
should be replaced with NULL test.

Also add check for return value of platform_get_resource().

Fixes: 54e19bc7

 ("net: qcom/emac: do not use devm on internal
phy pdev")
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Acked-by: Timur Tabi <timur@codeaurora.org>
Signed-off-by: David S. Miller <davem@davemloft.net>