ASoC: topology: Remove widgets from dobj list

Currently when we unload and reload machine driver few times we end with
corrupted list and try to cleanup no longer existing objects. Fix this
by removing dobj from the list.

Signed-off-by: Amadeusz Sławiński <amadeuszx.slawinski@intel.com>
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>