ASoC: do not close shared backend dailink

Multiple frontend dailinks may be connected to a backend
dailink at the same time. When one of frontend dailinks is
closed, the associated backend dailink should not be closed
if it is connected to other active frontend dailinks. Change
ensures that backend dailink is closed only after all
connected frontend dailinks are closed.

Signed-off-by: Gopikrishnaiah Anandan <agopik@codeaurora.org>
Signed-off-by: Banajit Goswami <bgoswami@codeaurora.org>
Signed-off-by: Patrick Lai <plai@codeaurora.org>
Signed-off-by: Mark Brown <broonie@kernel.org>
Cc: stable@vger.kernel.org