usb: dwc3: allow forcing a maximum speed

this is mainly for testing. In order to be able
to test if we're enumerating correctly on all
speeds, let that be controlled by a module
parameter.

Signed-off-by: Felipe Balbi <balbi@ti.com>
diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
index 46ed15b..807737a 100644
--- a/drivers/usb/dwc3/gadget.c
+++ b/drivers/usb/dwc3/gadget.c
@@ -1183,7 +1183,7 @@
 
 	reg = dwc3_readl(dwc->regs, DWC3_DCFG);
 	reg &= ~(DWC3_DCFG_SPEED_MASK);
-	reg |= DWC3_DCFG_SUPERSPEED;
+	reg |= dwc->maximum_speed;
 	dwc3_writel(dwc->regs, DWC3_DCFG, reg);
 
 	dwc->start_config_issued = false;