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

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.

Signed-off-by: Juergen Gross <[e-mail]>
Acked-by: David Vrabel <[e-mail]>

drivers/xen/xen-pciback/xenbus.c

···
 	int err = 0;
 	int num_devs;
 	int domain, bus, slot, func;
-	int substate;
+	unsigned int substate;
 	int i, len;
 	char state_str[64];
 	char dev_str[64];
···
 					 "configuration");
 			goto out;
 		}
-		err = xenbus_scanf(XBT_NIL, pdev->xdev->nodename, state_str,
-				   "%d", &substate);
-		if (err != 1)
-			substate = XenbusStateUnknown;
+		substate = xenbus_read_unsigned(pdev->xdev->nodename, state_str,
+						XenbusStateUnknown);
 
 		switch (substate) {
 		case XenbusStateInitialising: