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

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.

Cc: stable@vger.kernel.org
Fixes: 73cfd947dbdb ("net: ethernet: mtk_eth_soc: ppe: prevent ppe update for non-mtk devices")
Signed-off-by: Sven Eckelmann (Plasma Cloud) <se@simonwunderlich.de>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20260324-wed-crash-gmac0-disabled-v1-1-3bc388aee565@simonwunderlich.de
Signed-off-by: Jakub Kicinski <kuba@kernel.org>