net: stmmac: dwmac-intel-plat: fix error return code in intel_eth_plat_probe()

Fix to return a negative error code from the error handling
case instead of 0, as done elsewhere in this function.

Fixes: 9efc9b2b ("net: stmmac: Add dwmac-intel-plat for GBE driver")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Zhang Changzhong <zhangchangzhong@huawei.com>
Link: https://lore.kernel.org/r/1605249243-17262-1-git-send-email-zhangchangzhong@huawei.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>