usb: dwc3: Fix an IS_ERR() vs NULL check in dwc3_power_off_all_roothub_ports()

The ioremap() function doesn't return error pointers, it returns NULL on
error.  Update the check.

Fixes: 2d2a3349 ("usb: dwc3: Add workaround for host mode VBUS glitch when boot")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Acked-by: Thinh Nguyen <Thinh.Nguyen@synopsys.com>
Link: https://lore.kernel.org/r/71499112-4ed3-489a-9a56-b4a8ab89cd05@moroto.mountainSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/dwc3/host.c

@@ -35,7 +35,7 @@ static void dwc3_power_off_all_roothub_ports(struct dwc3 *dwc)
 	/* xhci regs is not mapped yet, do it temperary here */
 	if (dwc->xhci_resources[0].start) {
 		xhci_regs = ioremap(dwc->xhci_resources[0].start, DWC3_XHCI_REGS_END);
-		if (IS_ERR(xhci_regs)) {
+		if (!xhci_regs) {
 			dev_err(dwc->dev, "Failed to ioremap xhci_regs\n");
 			return;
 		}