ath79: also reduce spi-max-frequency for buffalo_wzr-hp-ag300h

In accordance to ebc090e420 ("ath79: reduce spi-max-frequency to 50 MHz")
this also reduces the spi-max-frequency to 50 MHz for the last remaining
device with higher frequency in ath79. This will save us from having a
single special case that will require adjustment when the spi driver for
this device is changed in the future.

Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>
Acked-by: Chuanhong Guo <gch981213@gmail.com>

target/linux/ath79/dts/ar7161_buffalo_wzr-hp-ag300h.dts

@@ -234,14 +234,14 @@
 	flash0: flash@0 {
 		compatible = "jedec,spi-nor";
 		reg = <0>;
-		spi-max-frequency = <104000000>;
+		spi-max-frequency = <50000000>;
 		m25p,fast-read;
 	};
 
 	flash1: flash@1 {
 		compatible = "jedec,spi-nor";
 		reg = <1>;
-		spi-max-frequency = <104000000>;
+		spi-max-frequency = <50000000>;
 		m25p,fast-read;
 	};
 };