ASoC: Intel: Atom: Fix message handling during drop stream

If a stream is being dropped, the period_elapsed received then after
need not be processed. Processing of the period_elapsed message causes
a time out in drop stream response processing. This patch adds a condition
to skip period_elapsed message processing if the stream is in INIT state.

Signed-off-by: Harsha Priya <harshapriya.n@intel.com>
Signed-off-by: Naveen M <naveen.m@intel.com>
Acked-by: Vinod Koul <vinod.koul@intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>