ARM: dts: stm32: add #clock-cells property to usbphyc node on stm32mp151

usbphyc is a 48Mhz clock provider: the clock can be used as clock source
for USB OTG. Add #clock-cells property to usbphyc node to reflect this
capability.
Signed-off-by: Amelie Delaunay <amelie.delaunay@foss.st.com>
Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>

arch/arm/boot/dts/stm32mp151.dtsi

@@ -1482,6 +1482,7 @@ iwdg2: watchdog@5a002000 {
 		usbphyc: usbphyc@5a006000 {
 			#address-cells = <1>;
 			#size-cells = <0>;
+			#clock-cells = <0>;
 			compatible = "st,stm32mp1-usbphyc";
 			reg = <0x5a006000 0x1000>;
 			clocks = <&rcc USBPHY_K>;