Running "dtbs_check" yells:
  '#clock-cells' is a dependency of 'clock-output-names'

...and sure enough the bindings say we should have "#clock-cells".
Add it.
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Fixes: 0b766e7f ("arm64: dts: qcom: sc7180: Add USB related nodes")
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Link: https://lore.kernel.org/r/20191212113540.3.Ia530e4065ca81f55ac8f89a400f6a0a084ff6712@changeidSigned-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>