xhci: Use device_iommu_mapped()

Replace the dev->iommu_group check with a proper function
call that better reprensents its purpose.

Cc: Mathias Nyman <mathias.nyman@intel.com>
Acked-by: NRobin Murphy <robin.murphy@arm.com>
Acked-by: NMathias Nyman <mathias.nyman@linux.intel.com>
Signed-off-by: NJoerg Roedel <jroedel@suse.de>

drivers/usb/host/xhci.c

@@ -244,7 +244,7 @@ static void xhci_zero_64b_regs(struct xhci_hcd *xhci)
 	 * an iommu. Doing anything when there is no iommu is definitely
 	 * unsafe...
 	 */
-	if (!(xhci->quirks & XHCI_ZERO_64B_REGS) || !dev->iommu_group)
+	if (!(xhci->quirks & XHCI_ZERO_64B_REGS) || !device_iommu_mapped(dev))
 		return;
 
 	xhci_info(xhci, "Zeroing 64bit base registers, expecting fault\n");