drivers/spi/spi.c: don't release the spi device twice

This was fixed by David Lamparter in v2.6.36-rc5 3486008 ("spi: free
children in spi_unregister_master, not siblings") and broken again in
v2.6.37-rc1~2^2~4 during the merge of 2b9603a0 ("spi: enable
spi_board_info to be registered after spi_master").

Signed-off-by: Sebastian Andrzej Siewior <[e-mail]>
Signed-off-by: David Lamparter <[e-mail]>
Cc: Grant Likely <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

drivers/spi/spi.c

···
 	list_del(&master->list);
 	mutex_unlock(&board_lock);
 
-	dummy = device_for_each_child(master->dev.parent, &master->dev,
-					__unregister);
+	dummy = device_for_each_child(&master->dev, NULL, __unregister);
 	device_unregister(&master->dev);
 }
 EXPORT_SYMBOL_GPL(spi_unregister_master);