ramips: increase spi frequency for Buffalo WCR-1166DS

Use higher frequency than current and up the speed to access to the
flash on WCR-1166DS.

Signed-off-by: INAGAKI Hiroshi <musashino.open@gmail.com>

target/linux/ramips/dts/mt7628an_buffalo_wcr-1166ds.dts

@@ -120,7 +120,7 @@
 	flash@0 {
 		compatible = "jedec,spi-nor";
 		reg = <0>;
-		spi-max-frequency = <10000000>;
+		spi-max-frequency = <40000000>;
 
 		partitions {
 			compatible = "fixed-partitions";