ramips: fix 2.4G wmac eeprom offset for TL-WR902AC v4

The eeprom data offset on 2.4GHz wmac is wrong. It is obvious that
this is a copy & paste issue.

Suggested-by: @cgm999 on openwrt#13969
Signed-off-by: Shiji Yang <yangshiji66@qq.com>
Link: openwrt#17263
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>

target/linux/ramips/dts/mt7628an_tplink_tl-wr902ac-v4.dts

@@ -108,7 +108,7 @@
 
 &wmac {
 	status = "okay";
-	nvmem-cells = <&eeprom_factory_28000>, <&macaddr_factory_f100 0>;
+	nvmem-cells = <&eeprom_factory_20000>, <&macaddr_factory_f100 0>;
 	nvmem-cell-names = "eeprom", "mac-address";
 };