ARM: dts: imx: Fix pca9547 i2c-mux node name

"make dtbs_check":

    arch/arm/boot/dts/imx53-ppd.dtb: i2c-switch@70: $nodename:0: 'i2c-switch@70' does not match '^(i2c-?)?mux'
	    From schema: Documentation/devicetree/bindings/i2c/i2c-mux-pca954x.yaml
    arch/arm/boot/dts/imx53-ppd.dtb: i2c-switch@70: Unevaluated properties are not allowed ('#address-cells', '#size-cells', 'i2c@0', 'i2c@1', 'i2c@2', 'i2c@3', 'i2c@4', 'i2c@5', 'i2c@6', 'i2c@7' were unexpected)
	    From schema: Documentation/devicetree/bindings/i2c/i2c-mux-pca954x.yaml

Fix this by renaming the PCA9547 node to "i2c-mux", to match the I2C bus
multiplexer/switch DT bindings and the Generic Names Recommendation in
the Devicetree Specification.
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm/boot/dts/imx53-ppd.dts

@@ -488,7 +488,7 @@ &i2c1 {
 	scl-gpios = <&gpio3 21 GPIO_ACTIVE_HIGH>;
 	status = "okay";
 
-	i2c-switch@70 {
+	i2c-mux@70 {
 		compatible = "nxp,pca9547";
 		#address-cells = <1>;
 		#size-cells = <0>;