usb: dwc3: Validate the maximum_speed parameter

Check that dwc->maximum_speed is set to a valid value. Also add an error
when we use it later if we encounter an invalid value.

Signed-off-by: John Youn <johnyoun@synopsys.com>
Signed-off-by: Felipe Balbi <balbi@kernel.org>
diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
index 482e6a1..3ac170f 100644
--- a/drivers/usb/dwc3/gadget.c
+++ b/drivers/usb/dwc3/gadget.c
@@ -1670,10 +1670,13 @@
 		case USB_SPEED_SUPER_PLUS:
 			reg |= DWC3_DSTS_SUPERSPEED_PLUS;
 			break;
-		case USB_SPEED_SUPER:	/* FALLTHROUGH */
-		case USB_SPEED_UNKNOWN:	/* FALTHROUGH */
 		default:
-			reg |= DWC3_DSTS_SUPERSPEED;
+			dev_err(dwc->dev, "invalid dwc->maximum_speed (%d)\n",
+				dwc->maximum_speed);
+			/* fall through */
+		case USB_SPEED_SUPER:
+			reg |= DWC3_DCFG_SUPERSPEED;
+			break;
 		}
 	}
 	dwc3_writel(dwc->regs, DWC3_DCFG, reg);