dt-bindings: phy: qcom,sc8280xp-qmp-usb3-uni: drop reference-clock source

The source clock for the reference clock is not used by the PHY directly
and should not be included in the devicetree binding.

Fixes: e8e58e29 ("dt-bindings: phy: qcom,qmp-usb: fix sc8280xp binding")
Signed-off-by: Johan Hovold <johan+linaro@kernel.org>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20221111093857.11360-2-johan+linaro@kernel.org


Signed-off-by: Vinod Koul <vkoul@kernel.org>