usb: dwc3: gadget: make sure HIRD threshold is 0 in superspeed

During superspeed, HIRD threshold should always
be zero. Curent driver wasn't making sure that
was the case.

Signed-off-by: Felipe Balbi <balbi@ti.com>
diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
index 3934d0a..df9749e 100644
--- a/drivers/usb/dwc3/gadget.c
+++ b/drivers/usb/dwc3/gadget.c
@@ -2289,6 +2289,10 @@
 		reg |= DWC3_DCTL_HIRD_THRES(12);
 
 		dwc3_writel(dwc->regs, DWC3_DCTL, reg);
+	} else {
+		reg = dwc3_readl(dwc->regs, DWC3_DCTL);
+		reg &= ~DWC3_DCTL_HIRD_THRES_MASK;
+		dwc3_writel(dwc->regs, DWC3_DCTL, reg);
 	}
 
 	dep = dwc->eps[0];