arm64: dts: microchip: sparx5_pcb135: align I2C mux node name with bindings

DT schema expects node names to match certain.  This fixes dtbs_check
warnings like:

  sparx5_pcb135_emmc.dtb: i2c0-imux@0: $nodename:0: 'i2c0-imux@0' does not match '^(i2c-?)?mux'

and dtc W=1 warnings:

  sparx5_pcb135_board.dtsi:132.25-137.4: Warning (simple_bus_reg): /axi@600000000/i2c0-imux@0: missing or empty reg/ranges property
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Reviewed-by: Steen Hegelund <Steen.Hegelund@microchip.com>
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>

arch/arm64/boot/dts/microchip/sparx5_pcb135_board.dtsi

@@ -129,7 +129,7 @@ &sgpio2 {
 };
 
 &axi {
-	i2c0_imux: i2c0-imux@0 {
+	i2c0_imux: i2c-mux {
 		compatible = "i2c-mux-pinctrl";
 		#address-cells = <1>;
 		#size-cells = <0>;