net: ll_temac: Use devm_platform_ioremap_resource_byname()

platform_get_resource() may fail and return NULL, so we had better
check its return value to avoid a NULL pointer dereference a bit later
in the code. Fix it to use devm_platform_ioremap_resource_byname()
instead of calling platform_get_resource_byname() and devm_ioremap().

Fixes: 8425c41d

 ("net: ll_temac: Extend support to non-device-tree platforms")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Wang Hai <wanghai38@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>