ath79: ar913x: fix eth pll register

PLL for eth0 internal clock on ar913x is at 0x18050014
and AR913X_ETH0_PLL_SHIFT is 20 instead of 17

Signed-off-by: Chuanhong Guo <gch981213@gmail.com>

target/linux/ath79/dts/ar9132.dtsi

@@ -189,7 +189,7 @@
 	reg = <0x19000000 0x200
 		0x18070000 0x4>;
 	pll-data = <0x1a000000 0x13000a44 0x00441099>;
-	pll-reg = <0x4 0x10 17>;
+	pll-reg = <0x4 0x14 20>;
 	pll-handle = <&pll>;
 	resets = <&rst 9>;
 	reset-names = "mac";