ARM: dts: NSP: Update ethernet switch node name

Update the switch unit name from srab to ethernet-switch, allowing us
to fix warnings such as:

CHECK arch/arm/boot/dts/bcm4708-buffalo-wzr-1750dhp.dt.yaml
arch/arm/boot/dts/bcm4708-buffalo-wzr-1750dhp.dt.yaml:
srab@18007000: $nodename:0: 'srab@18007000' does not match
'^(ethernet-)?switch(@.*)?$'
From schema:
Documentation/devicetree/bindings/net/dsa/b53.yaml

Reviewed-by: Vladimir Oltean <[e-mail]>
Signed-off-by: Florian Fainelli <[e-mail]>

arch/arm/boot/dts/bcm-nsp.dtsi

···
 			clock-names = "apb_pclk";
 		};
 
-		srab: srab@36000 {
+		srab: ethernet-switch@36000 {
 			compatible = "brcm,nsp-srab";
 			reg = <0x36000 0x1000>,
 			      <0x3f308 0x8>,