net: fec_mxc: avoid transfer dev_id -1 to get mac address from fuse

Avoid transfer parameter dev_id value with "-1" to .fec_get_hwaddr(),
it should transfer fec->dev_id to get mac address from fuse.

Signed-off-by: Fugang Duan <fugang.duan@nxp.com>
Signed-off-by: Peng Fan <peng.fan@nxp.com>
Cc: Joe Hershberger <joe.hershberger@ni.com>
Acked-by: Stefano Babic <sbabic@denx.de>