ACPI / hotplug / PCI: Drop WARN_ON() from acpiphp_enumerate_slots()

The WARN_ON() in acpiphp_enumerate_slots() triggers unnecessarily for
devices whose bridges are going to be handled by native PCIe hotplug
(pciehp) and the simplest way to prevent that from happening is to
drop the WARN_ON().

References: https://bugzilla.kernel.org/show_bug.cgi?id=62831
Reported-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Author: rafaeljw

drivers/pci/hotplug/acpiphp_glue.c

@@ -994,12 +994,13 @@ void acpiphp_enumerate_slots(struct pci_bus *bus)
 
 		/*
 		 * This bridge should have been registered as a hotplug function
-		 * under its parent, so the context has to be there.  If not, we
-		 * are in deep goo.
+		 * under its parent, so the context should be there, unless the
+		 * parent is going to be handled by pciehp, in which case this
+		 * bridge is not interesting to us either.
 		 */
 		mutex_lock(&acpiphp_context_lock);
 		context = acpiphp_get_context(handle);
-		if (WARN_ON(!context)) {
+		if (!context) {
 			mutex_unlock(&acpiphp_context_lock);
 			put_device(&bus->dev);
 			pci_dev_put(bridge->pci_dev);