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: 450b9e9fabd8 ("usb: dwc3: gadget: Set speed only up to the max supported")
Cc: <[e-mail]>
Signed-off-by: Thinh Nguyen <[e-mail]>
Link: https://lore.kernel.org/r/55ac[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/usb/dwc3/gadget.c

···
 	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 &&