PCI: Introduce pci_resource_n()

Introduce pci_resource_n() and replace open-coded implementations of it
in pci.h.

Link: https://lore.kernel.org/r/20230330162434.35055-3-andriy.shevchenko@linux.intel.comSigned-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>

include/linux/pci.h

@@ -1994,14 +1994,13 @@ int pci_iobar_pfn(struct pci_dev *pdev, int bar, struct vm_area_struct *vma);
  * These helpers provide future and backwards compatibility
  * for accessing popular PCI BAR info
  */
-#define pci_resource_start(dev, bar)	((dev)->resource[(bar)].start)
-#define pci_resource_end(dev, bar)	((dev)->resource[(bar)].end)
-#define pci_resource_flags(dev, bar)	((dev)->resource[(bar)].flags)
-#define pci_resource_len(dev,bar) \
-	((pci_resource_end((dev), (bar)) == 0) ? 0 :	\
-							\
-	 (pci_resource_end((dev), (bar)) -		\
-	  pci_resource_start((dev), (bar)) + 1))
+#define pci_resource_n(dev, bar)	(&(dev)->resource[(bar)])
+#define pci_resource_start(dev, bar)	(pci_resource_n(dev, bar)->start)
+#define pci_resource_end(dev, bar)	(pci_resource_n(dev, bar)->end)
+#define pci_resource_flags(dev, bar)	(pci_resource_n(dev, bar)->flags)
+#define pci_resource_len(dev,bar)					\
+	(pci_resource_end((dev), (bar)) ? 				\
+	 resource_size(pci_resource_n((dev), (bar))) : 0)
 
 /*
  * Similar to the helpers above, these manipulate per-pci_dev