arm64: dts: broadcom: bcm4908: use proper NAND binding

BCM4908 has controller that needs different IRQ handling just like the
BCM63138. Describe it properly.

On Linux this change fixes:
brcmstb_nand ff801800.nand: timeout waiting for command 0x9
brcmstb_nand ff801800.nand: intfc status d0000000
Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>

arch/arm64/boot/dts/broadcom/bcm4908/bcm4908.dtsi

@@ -164,7 +164,7 @@ uart0: serial@640 {
 		nand@1800 {
 			#address-cells = <1>;
 			#size-cells = <0>;
-			compatible = "brcm,brcmnand-v7.1", "brcm,brcmnand";
+			compatible = "brcm,nand-bcm63138", "brcm,brcmnand-v7.1", "brcm,brcmnand";
 			reg = <0x1800 0x600>, <0x2000 0x10>;
 			reg-names = "nand", "nand-int-base";
 			interrupts = <GIC_SPI 37 IRQ_TYPE_LEVEL_HIGH>;