dt-bindings: phy: ti,phy-j721e-wiz: document clock-output-names

dt-bindings: phy: ti,phy-j721e-wiz: document clock-output-names

Document the clock-output-names property of clock children, even though
the nodes are actually deprecated, to fix dtbs_check warnings like:

  k3-j7200-common-proc-board.dtb: wiz@5060000: refclk-dig: 'clock-output-names' does not match any of the regexes: 'pinctrl-[0-9]+'

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20230404190115.546973-5-krzysztof.kozlowski@linaro.org
Signed-off-by: Vinod Koul <vkoul@kernel.org>