staging: greybus: arche-platform: fix device reference leak

Make sure to drop the device reference taken by of_find_device_by_node()
before returning from arche_platform_change_state().

Note that this code is expected to be removed, but let's fix up the leak
nonetheless.

Fixes: 886aba558b9e ("greybus: arche-platform: Export fn to allow...")
Signed-off-by: Johan Hovold <[e-mail]>
Acked-by: Viresh Kumar <[e-mail]>
Reviewed-by: Vaibhav Hiremath <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/staging/greybus/arche-platform.c

···
 exit:
 	spin_unlock_irqrestore(&arche_pdata->wake_lock, flags);
 	mutex_unlock(&arche_pdata->platform_state_mutex);
+	put_device(&pdev->dev);
 	of_node_put(np);
 	return ret;
 }