usb: dwc2: gadget: Make use of GINTMSK2

The value obtained from GINTSTS2 should be masked with the GINTMSK2
value.  Looks like this has been broken since
dwc2_gadget_wkup_alert_handler() was added back in 2018.

Also fixes the following W=1 warning:

 drivers/usb/dwc2/gadget.c: In function ‘dwc2_gadget_wkup_alert_handler’:
 drivers/usb/dwc2/gadget.c:259:6: warning: variable ‘gintmsk2’ set but not used [-Wunused-but-set-variable]
 259 | u32 gintmsk2;
 | ^~~~~~~~

Cc: Ben Dooks <ben@simtec.co.uk>
Fixes: 187c5298 ("usb: dwc2: gadget: Add handler for WkupAlert interrupt")
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Acked-by: Minas Harutyunyan <hminas@synopsys.com>
Link: https://lore.kernel.org/r/20200715093209.3165641-2-lee.jones@linaro.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/dwc2/gadget.c

@@ -260,6 +260,7 @@ static void dwc2_gadget_wkup_alert_handler(struct dwc2_hsotg *hsotg)
 
 	gintsts2 = dwc2_readl(hsotg, GINTSTS2);
 	gintmsk2 = dwc2_readl(hsotg, GINTMSK2);
+	gintsts2 &= gintmsk2;
 
 	if (gintsts2 & GINTSTS2_WKUP_ALERT_INT) {
 		dev_dbg(hsotg->dev, "%s: Wkup_Alert_Int\n", __func__);