ACPI / hotplug / PCI: Fix sparse non static symbol warning

Fixes the following sparse warning:

drivers/pci/hotplug/acpiphp_glue.c:923:6: warning:
 symbol 'acpiphp_drop_bridge' was not declared. Should it be static?
Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/pci/hotplug/acpiphp_glue.c

@@ -920,7 +920,7 @@ void acpiphp_enumerate_slots(struct pci_bus *bus)
 	kfree(bridge);
 }
 
-void acpiphp_drop_bridge(struct acpiphp_bridge *bridge)
+static void acpiphp_drop_bridge(struct acpiphp_bridge *bridge)
 {
 	if (pci_is_root_bus(bridge->pci_bus)) {
 		struct acpiphp_root_context *root_context;