ACPI: bus: Remove the unneeded result variable

Return the value from driver_register() directly instead of storing it
in another redundant variable.

Reported-by: Zeal Robot <zealci@zte.com.cn>
Signed-off-by: ye xingchen <ye.xingchen@zte.com.cn>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/acpi/bus.c

@@ -973,16 +973,13 @@ EXPORT_SYMBOL_GPL(acpi_driver_match_device);
  */
 int acpi_bus_register_driver(struct acpi_driver *driver)
 {
-	int ret;
-
 	if (acpi_disabled)
 		return -ENODEV;
 	driver->drv.name = driver->name;
 	driver->drv.bus = &acpi_bus_type;
 	driver->drv.owner = driver->owner;
 
-	ret = driver_register(&driver->drv);
-	return ret;
+	return driver_register(&driver->drv);
 }
 
 EXPORT_SYMBOL(acpi_bus_register_driver);