dt-bindings: mfd: brcm,cru: Rename pinctrl node

This matches pinctrl.yaml requirement and fixes:

Documentation/devicetree/bindings/mfd/brcm,cru.example.dt.yaml: pin-controller@1c0: $nodename:0: 'pin-controller@1c0' does not match '^(pinctrl|pinmux)(@[0-9a-f]+)?$'
        From schema: Documentation/devicetree/bindings/pinctrl/brcm,ns-pinmux.yaml

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20220216112928.5330-1-zajec5@gmail.com