arm64: dts: qcom: update usb qmp phy clock-cells property

The top-level node doesn't provide any clocks, the subnode provides a
single clock with of_clk_hw_simple_get.

Signed-off-by: Jonathan Marek <jonathan@marek.ca>
Link: https://lore.kernel.org/r/20201123143705.14277-1-jonathan@marek.ca


Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>