ACPI: introduce a function to find the first physical device

Factor out the code that finds the first physical device
of a given ACPI device.  It is used in several places.

Signed-off-by: Aleksey Makarov <aleksey.makarov@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
diff --git a/drivers/acpi/acpi_platform.c b/drivers/acpi/acpi_platform.c
index 296b7a1..c3af108 100644
--- a/drivers/acpi/acpi_platform.c
+++ b/drivers/acpi/acpi_platform.c
@@ -43,7 +43,6 @@
 struct platform_device *acpi_create_platform_device(struct acpi_device *adev)
 {
 	struct platform_device *pdev = NULL;
-	struct acpi_device *acpi_parent;
 	struct platform_device_info pdevinfo;
 	struct resource_entry *rentry;
 	struct list_head resource_list;
@@ -82,22 +81,8 @@
 	 * attached to it, that physical device should be the parent of the
 	 * platform device we are about to create.
 	 */
-	pdevinfo.parent = NULL;
-	acpi_parent = adev->parent;
-	if (acpi_parent) {
-		struct acpi_device_physical_node *entry;
-		struct list_head *list;
-
-		mutex_lock(&acpi_parent->physical_node_lock);
-		list = &acpi_parent->physical_node_list;
-		if (!list_empty(list)) {
-			entry = list_first_entry(list,
-					struct acpi_device_physical_node,
-					node);
-			pdevinfo.parent = entry->dev;
-		}
-		mutex_unlock(&acpi_parent->physical_node_lock);
-	}
+	pdevinfo.parent = adev->parent ?
+		acpi_get_first_physical_node(adev->parent) : NULL;
 	pdevinfo.name = dev_name(&adev->dev);
 	pdevinfo.id = -1;
 	pdevinfo.res = resources;