xen/pciback: use resource_size()

Use resource_size function on resource object
 instead of explicit computation.

 The semantic patch that makes this output is available
 in scripts/coccinelle/api/resource_size.cocci.

 More information about semantic patching is available at
 http://coccinelle.lip6.fr/

Signed-off-by: Thomas Meyer <thomas@m3y3r.de>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

drivers/xen/xen-pciback/conf_space_header.c

@@ -187,7 +187,7 @@ static inline void read_dev_bar(struct pci_dev *dev,
 
 	bar_info->val = res[pos].start |
 			(res[pos].flags & PCI_REGION_FLAG_MASK);
-	bar_info->len_val = res[pos].end - res[pos].start + 1;
+	bar_info->len_val = resource_size(&res[pos]);
 }
 
 static void *bar_init(struct pci_dev *dev, int offset)