PCI: Improve pci_scan_bridge() and pci_scan_bridge_extend() doc

It is not immediately clear what the two functions actually return so
add kernel-doc comment explaining it a bit better.
Suggested-by: NBjorn Helgaas <bhelgaas@google.com>
Signed-off-by: NMika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: NBjorn Helgaas <bhelgaas@google.com>
Reviewed-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: NAndy Shevchenko <andriy.shevchenko@linux.intel.com>

drivers/pci/probe.c

@@ -999,6 +999,8 @@ static unsigned int pci_scan_child_bus_extend(struct pci_bus *bus,
  * already configured by the BIOS and after we are done with all of
  * them, we proceed to assigning numbers to the remaining buses in
  * order to avoid overlaps between old and new bus numbers.
+ *
+ * Return: New subordinate number covering all buses behind this bridge.
  */
 static int pci_scan_bridge_extend(struct pci_bus *bus, struct pci_dev *dev,
 				  int max, unsigned int available_buses,
@@ -1231,6 +1233,8 @@ static int pci_scan_bridge_extend(struct pci_bus *bus, struct pci_dev *dev,
  * already configured by the BIOS and after we are done with all of
  * them, we proceed to assigning numbers to the remaining buses in
  * order to avoid overlaps between old and new bus numbers.
+ *
+ * Return: New subordinate number covering all buses behind this bridge.
  */
 int pci_scan_bridge(struct pci_bus *bus, struct pci_dev *dev, int max, int pass)
 {