arm64: dts: imx8qxp: fix mbox-cells

Currently lsio_mu1 is used by Linux Kernel with mbox-cells as 2, but
actually mu0-4 could be used to communicate with SCU. So fix the
mbox-cells.
Signed-off-by: Peng Fan <peng.fan@nxp.com>
Reviewed-by: Dong Aisheng <aisheng.dong@nxp.com>
Fixes: 3d91ba65 ("arm64: dts: imx: add imx8qxp support")
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm64/boot/dts/freescale/imx8qxp.dtsi

@@ -358,7 +358,7 @@ lsio_mu0: mailbox@5d1b0000 {
 			compatible = "fsl,imx8qxp-mu", "fsl,imx6sx-mu";
 			reg = <0x5d1b0000 0x10000>;
 			interrupts = <GIC_SPI 176 IRQ_TYPE_LEVEL_HIGH>;
-			#mbox-cells = <0>;
+			#mbox-cells = <2>;
 			status = "disabled";
 		};
 
@@ -373,7 +373,7 @@ lsio_mu3: mailbox@5d1e0000 {
 			compatible = "fsl,imx8qxp-mu", "fsl,imx6sx-mu";
 			reg = <0x5d1e0000 0x10000>;
 			interrupts = <GIC_SPI 179 IRQ_TYPE_LEVEL_HIGH>;
-			#mbox-cells = <0>;
+			#mbox-cells = <2>;
 			status = "disabled";
 		};
 
@@ -381,7 +381,7 @@ lsio_mu4: mailbox@5d1f0000 {
 			compatible = "fsl,imx8qxp-mu", "fsl,imx6sx-mu";
 			reg = <0x5d1f0000 0x10000>;
 			interrupts = <GIC_SPI 180 IRQ_TYPE_LEVEL_HIGH>;
-			#mbox-cells = <0>;
+			#mbox-cells = <2>;
 			status = "disabled";
 		};