dt-bindings: phy: qcom,qmp: Shift '#clock-cells' property to phy (child) node

Since the clock comes out of the phy (child) node,
so clocks are actually not provided by the parent device.
The qmp-phy dt-bindings specify the same incorrectly at
present. Fix the same.

This change helps fix the following 'make dtbs_check' warning(s):

sm8350-microsoft-surface-duo2.dt.yaml: phy@1d87000:
  '#clock-cells' is a required property

Cc: Bjorn Andersson <bjorn.andersson@linaro.org>
Cc: Vinod Koul <vkoul@kernel.org>
Cc: Rob Herring <robh+dt@kernel.org>
Signed-off-by: Bhupesh Sharma <bhupesh.sharma@linaro.org>