riscv: dts: sifive: use only generic JEDEC SPI NOR flash compatible

The compatible "issi,is25wp256" is undocumented and instead only a
generic jedec,spi-nor should be used (if appropriate).
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Link: https://lore.kernel.org/r/20210920130248.145058-1-krzysztof.kozlowski@canonical.com

arch/riscv/boot/dts/sifive/hifive-unleashed-a00.dts

@@ -63,7 +63,7 @@ &i2c0 {
 &qspi0 {
 	status = "okay";
 	flash@0 {
-		compatible = "issi,is25wp256", "jedec,spi-nor";
+		compatible = "jedec,spi-nor";
 		reg = <0>;
 		spi-max-frequency = <50000000>;
 		m25p,fast-read;

arch/riscv/boot/dts/sifive/hifive-unmatched-a00.dts

@@ -211,7 +211,7 @@ vdd_ldo11: ldo11 {
 &qspi0 {
 	status = "okay";
 	flash@0 {
-		compatible = "issi,is25wp256", "jedec,spi-nor";
+		compatible = "jedec,spi-nor";
 		reg = <0>;
 		spi-max-frequency = <50000000>;
 		m25p,fast-read;