ath79: bump SPI frequency of Senao qca955x routers

All boards using this DTSI are expected to have
the same 16 MB MX25L12845EMI-10G flash chip,
or a larger one which can also use 40 MHz frequency.

Signed-off-by: Michael Pratt <[email protected]>

target/linux/ath79/dts/qca955x_senao_router-dual.dtsi

@@ -55,7 +55,7 @@
 	flash@0 {
 		compatible = "jedec,spi-nor";
 		reg = <0>;
-		spi-max-frequency = <25000000>;
+		spi-max-frequency = <40000000>;
 
 		partitions {
 			compatible = "fixed-partitions";