dt-bindings: mt8173-mtu3: add reference clock

add a reference clock for compatibility

Signed-off-by: Chunfeng Yun <chunfeng.yun@mediatek.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/devicetree/bindings/usb/mt8173-mtu3.txt

@@ -10,7 +10,7 @@ Required properties:
  - vusb33-supply : regulator of USB avdd3.3v
  - clocks : a list of phandle + clock-specifier pairs, one for each
 	entry in clock-names
- - clock-names : must contain "sys_ck" for clock of controller;
+ - clock-names : must contain "sys_ck" and "ref_ck" for clock of controller;
 	"wakeup_deb_p0" and "wakeup_deb_p1" are optional, they are
 	depends on "mediatek,enable-wakeup"
  - phys : a list of phandle + phy specifier pairs
@@ -56,10 +56,10 @@ ssusb: usb@11271000 {
 	phys = <&phy_port0 PHY_TYPE_USB3>,
 	       <&phy_port1 PHY_TYPE_USB2>;
 	power-domains = <&scpsys MT8173_POWER_DOMAIN_USB>;
-	clocks = <&topckgen CLK_TOP_USB30_SEL>,
+	clocks = <&topckgen CLK_TOP_USB30_SEL>, <&clk26m>,
 		 <&pericfg CLK_PERI_USB0>,
 		 <&pericfg CLK_PERI_USB1>;
-	clock-names = "sys_ck",
+	clock-names = "sys_ck", "ref_ck",
 		      "wakeup_deb_p0",
 		      "wakeup_deb_p1";
 	vusb33-supply = <&mt6397_vusb_reg>;
@@ -79,8 +79,8 @@ ssusb: usb@11271000 {
 		reg-names = "mac";
 		interrupts = <GIC_SPI 115 IRQ_TYPE_LEVEL_LOW>;
 		power-domains = <&scpsys MT8173_POWER_DOMAIN_USB>;
-		clocks = <&topckgen CLK_TOP_USB30_SEL>;
-		clock-names = "sys_ck";
+		clocks = <&topckgen CLK_TOP_USB30_SEL>, <&clk26m>;
+		clock-names = "sys_ck", "ref_ck";
 		vusb33-supply = <&mt6397_vusb_reg>;
 		status = "disabled";
 	};