ramips: Add missing chunked-io directive to W2914NSV2.dtsi

Fix bug that LEDE failed to boot with this message:

WARNING: CPU: 2 PID: 1 at drivers/spi/spi-mt7621.c:214
mt7621_spi_transfer_one_message+0x28c/0x620()

Signed-off-by: Yong-hyu, Ban <perillamint@gentoo.moe>

target/linux/ramips/dts/W2914NSV2.dtsi

@@ -55,6 +55,7 @@
 		compatible = "jedec,spi-nor";
 		reg = <0>;
 		spi-max-frequency = <10000000>;
+		m25p,chunked-io = <32>;
 
 		partition@0 {
 			label = "u-boot";