ACPI: fix single linked list manipulation

Fix single linked list manipulation for sub_driver.  If the remving entry
is not on the head of the sub_driver list, it goes into infinate loop.

Though that infinite loop doesn't happen.  Because the only user of
acpi_pci_register_dirver() is acpiphp.
Signed-off-by: NAkinobu Mita <akinobu.mita@gmail.com>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLen Brown <len.brown@intel.com>

drivers/acpi/pci_root.c

@@ -98,11 +98,12 @@ void acpi_pci_unregister_driver(struct acpi_pci_driver *driver)
 
 	struct acpi_pci_driver **pptr = &sub_driver;
 	while (*pptr) {
-		if (*pptr != driver)
-			continue;
-		*pptr = (*pptr)->next;
-		break;
+		if (*pptr == driver)
+			break;
+		pptr = &(*pptr)->next;
 	}
+	BUG_ON(!*pptr);
+	*pptr = (*pptr)->next;
 
 	if (!driver->remove)
 		return;