ramips: fix WHR-600D eeprom dt property

Fix the PCIe 5GHz wireless by using the ralink mtd-eeprom property as
this board have a RT5592 and uses the rt2x00 driver. The mediathek
device tree bindings do not work here.

Fixes: FS#691
Fixes: d8dd207ea6f2 ("ramips: use the ralink,mtd-eeprom device tree property")
Signed-off-by: Mathias Kresin <dev@kresin.me>