net: fec: set dev->seq to priv->dev_id

To platforms has two enet interface, using dev->seq could
avoid conflict.

i.MX6UL/ULL evk board net get the wrong MAC address from fuse,
eth1 get MAC0 address, eth0 get MAC1 address from fuse. Set the
priv->dev_id to device->seq as the real net interface alias id then
.fec_get_hwaddr() read the related MAC address from fuse.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>