usb: xhci-mtk: add reference clock

usually, the reference clock comes from 26M oscillator directly,
but some SoCs are not, add it for compatibility.

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

drivers/usb/host/xhci-mtk.h

@@ -124,6 +124,7 @@ struct xhci_hcd_mtk {
 	struct regulator *vusb33;
 	struct regulator *vbus;
 	struct clk *sys_clk;	/* sys and mac clock */
+	struct clk *ref_clk;
 	struct clk *wk_deb_p0;	/* port0's wakeup debounce clock */
 	struct clk *wk_deb_p1;
 	struct regmap *pericfg;