lantiq: fix mac address increments

lantiq: fix mac address increments

Use the same mac address increment in device tree source file and
userspace.

Don't add a mac address increment to either the only mtd mac-address or
to all mac-addresses.

Fix a typo in the TDW89X0.dtsi file to add an increment.

Signed-off-by: Mathias Kresin <dev@kresin.me>