xen: make use of xenbus_read_unsigned() in xen-pcifront

Use xenbus_read_unsigned() instead of xenbus_scanf() when possible.
This requires to change the type of the read from int to unsigned,
but this case has been wrong before: negative values are not allowed
for the modified case.

Cc: bhelgaas@google.com
Cc: linux-pci@vger.kernel.org

Signed-off-by: Juergen Gross <jgross@suse.com>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: David Vrabel <david.vrabel@citrix.com>

drivers/pci/xen-pcifront.c

@@ -1038,10 +1038,8 @@ static int pcifront_detach_devices(struct pcifront_device *pdev)
 			err = -ENOMEM;
 			goto out;
 		}
-		err = xenbus_scanf(XBT_NIL, pdev->xdev->otherend, str, "%d",
-				   &state);
-		if (err != 1)
-			state = XenbusStateUnknown;
+		state = xenbus_read_unsigned(pdev->xdev->otherend, str,
+					     XenbusStateUnknown);
 
 		if (state != XenbusStateClosing)
 			continue;