arm64: dts: qcom: sc7180: Add "#clock-cells" property to usb_1_ssphy

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>

arch/arm64/boot/dts/qcom/sc7180.dtsi

@@ -1020,6 +1020,7 @@ usb_1_ssphy: lanes@88e9200 {
 				      <0 0x088e9600 0 0x128>,
 				      <0 0x088e9800 0 0x200>,
 				      <0 0x088e9a00 0 0x18>;
+				#clock-cells = <0>;
 				#phy-cells = <0>;
 				clocks = <&gcc GCC_USB3_PRIM_PHY_PIPE_CLK>;
 				clock-names = "pipe0";