dt-bindings: net: dsa: nxp,sja1105: Add optional clock

Add optional clock for OSC_IN and fix the below CHECK_DTBS warnings:
arch/arm/boot/dts/nxp/imx/imx6qp-prtwd3.dtb: switch@0 (nxp,sja1105q): Unevaluated properties are not allowed ('clocks' was unexpected)

Signed-off-by: Frank Li <[e-mail]>
Acked-by: Conor Dooley <[e-mail]>
Reviewed-by: Vladimir Oltean <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

Documentation/devicetree/bindings/net/dsa/nxp,sja1105.yaml

···
       therefore discouraged.
     maxItems: 1
 
+  clocks:
+    maxItems: 1
+
   spi-cpha: true
   spi-cpol: true