net: ethernet: mtk_ppe: avoid NULL deref when gmac0 is disabled

In the Linux kernel, the following vulnerability has been resolved:

net: ethernet: mtk_ppe: avoid NULL deref when gmac0 is disabled

If the gmac0 is disabled, the precheck for a valid ingress device will

cause a NULL pointer deref and crash the system. This happens because

eth->netdev[0] will be NULL but the code will directly try to access

netdev_ops.

Instead of just checking for the first net_device, it must be checked if

any of the mtk_eth net_devices is matching the netdev_ops of the ingress

device.