ACPI: dock: convert acpi_evaluate_object() to acpi_evaluate_integer()

acpi_evaluate_integer() is an ACPI API introduced to evaluate an
ACPI control method that is known to have an integer return value.
This API can simplify the code because the calling function does not need to
use the specified acpi_buffer structure required by acpi_evaluate_object();

Convert acpi_evaluate_object() to acpi_evaluate_integer()
in drivers/acpi/dock.c in this patch.

Signed-off-by: Zhang Rui <rui.zhang@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
diff --git a/drivers/acpi/dock.c b/drivers/acpi/dock.c
index 05ea4be..ca86c1c 100644
--- a/drivers/acpi/dock.c
+++ b/drivers/acpi/dock.c
@@ -441,7 +441,7 @@
 	acpi_status status;
 	struct acpi_object_list arg_list;
 	union acpi_object arg;
-	struct acpi_buffer buffer = { ACPI_ALLOCATE_BUFFER, NULL };
+	unsigned long long value;
 
 	acpi_handle_info(ds->handle, "%s\n", dock ? "docking" : "undocking");
 
@@ -450,12 +450,10 @@
 	arg_list.pointer = &arg;
 	arg.type = ACPI_TYPE_INTEGER;
 	arg.integer.value = dock;
-	status = acpi_evaluate_object(ds->handle, "_DCK", &arg_list, &buffer);
+	status = acpi_evaluate_integer(ds->handle, "_DCK", &arg_list, &value);
 	if (ACPI_FAILURE(status) && status != AE_NOT_FOUND)
 		acpi_handle_err(ds->handle, "Failed to execute _DCK (0x%x)\n",
 				status);
-
-	kfree(buffer.pointer);
 }
 
 static inline void dock(struct dock_station *ds)