usb: dwc3: gadget: Use max speed if unspecified

If the gadget driver doesn't specify a max_speed, then use the
controller's maximum supported speed as default. For DWC_usb32 IP, the
gadget's speed maybe limited to gen2x1 rate only if the driver's
max_speed is unknown. This scenario should not occur with the current
implementation since the default gadget driver's max_speed should always
be specified. However, to make the driver more robust and help with
readability, let's cover all the scenarios in __dwc3_gadget_set_speed().

Fixes: 450b9e9 ("usb: dwc3: gadget: Set speed only up to the max supported")
Cc: <stable@vger.kernel.org>
Signed-off-by: Thinh Nguyen <Thinh.Nguyen@synopsys.com>
Link: https://lore.kernel.org/r/55ac7001af73bfe9bc750c6446ef4ac8cf6f9313.1615254129.git.Thinh.Nguyen@synopsys.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/dwc3/gadget.c

@@ -2083,7 +2083,7 @@ static void __dwc3_gadget_set_speed(struct dwc3 *dwc)
 	u32			reg;
 
 	speed = dwc->gadget_max_speed;
-	if (speed > dwc->maximum_speed)
+	if (speed == USB_SPEED_UNKNOWN || speed > dwc->maximum_speed)
 		speed = dwc->maximum_speed;
 
 	if (speed == USB_SPEED_SUPER_PLUS &&