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

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>