fm-eth: use fdt_status_disabled() function in ft_fixup_port()

We have a dedicated function for setting the node status now, so use it.
Also improve a comment and fix the type of the phandle variable.

Signed-off-by: Timur Tabi <timur@freescale.com>
Signed-off-by: Andy Fleming <afleming@freescale.com>