ARM: dts: am335x-phycore-som: Update compatible string for spi nor

As we may have different SPI NOR flashes with 8MB populated on
phyCORE-AM335x SOM, set the "jedec,spi-nor" SPI Flash compatible string.
Signed-off-by: Teresa Remmet <t.remmet@phytec.de>
Signed-off-by: Tony Lindgren <tony@atomide.com>

arch/arm/boot/dts/am335x-phycore-som.dtsi

@@ -341,7 +341,7 @@ &spi0 {
 	status = "okay";
 
 	serial_flash: m25p80@0 {
-		compatible = "m25p80";
+		compatible = "jedec,spi-nor";
 		spi-max-frequency = <48000000>;
 		reg = <0x0>;
 		m25p,fast-read;