usb: dwc3: qcom: suppress unused-variable warning

The dwc3_qcom_read_usb2_speed() helper is now only called when the
controller is acting as host, but the compiler will warn that the hcd
variable is unused in gadget-only W=1 builds.

Fixes: c06795f1 ("usb: dwc3: qcom: fix gadget-only builds")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Johan Hovold <johan+linaro@kernel.org>
Link: https://lore.kernel.org/r/20220822100550.3039-1-johan+linaro@kernel.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/dwc3/dwc3-qcom.c

@@ -310,7 +310,7 @@ static enum usb_device_speed dwc3_qcom_read_usb2_speed(struct dwc3_qcom *qcom)
 {
 	struct dwc3 *dwc = platform_get_drvdata(qcom->dwc3);
 	struct usb_device *udev;
-	struct usb_hcd *hcd;
+	struct usb_hcd __maybe_unused *hcd;
 
 	/*
 	 * FIXME: Fix this layering violation.