ACPI: bus: Set driver_data to NULL every time .add() fails

Most ACPI drivers set driver_data in their .add() callbacks, but usually
they don't clear it in the error code path.

Set driver_data to NULL in acpi_device_probe() to prevent stale pointers
from staying around.
Signed-off-by: Michal Wilczynski <michal.wilczynski@intel.com>
[ rjw: Subject and changelog edits ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/acpi/bus.c

@@ -1029,8 +1029,10 @@ static int acpi_device_probe(struct device *dev)
 		return -ENOSYS;
 
 	ret = acpi_drv->ops.add(acpi_dev);
-	if (ret)
+	if (ret) {
+		acpi_dev->driver_data = NULL;
 		return ret;
+	}
 
 	pr_debug("Driver [%s] successfully bound to device [%s]\n",
 		 acpi_drv->name, acpi_dev->pnp.bus_id);