ath79: increase WS-AP3610 SPI frequency

The M25P80 used on the Siemens WS-AP3610 supports clock speeds up to 54
MHz. Thus, we can safely increase the maximum SPI frequency the flash
chip is controlled at to 50 MHz, increasing transfer speed.

Signed-off-by: David Bauer <mail@david-bauer.net>

target/linux/ath79/dts/ar7161_siemens_ws-ap3610.dts

@@ -110,7 +110,7 @@
 	flash@0 {
 		compatible = "jedec,spi-nor";
 		reg = <0>;
-		spi-max-frequency = <25000000>;
+		spi-max-frequency = <50000000>;
 
 		partitions {
 			compatible = "fixed-partitions";