ASoC: PCM: Release memory allocated for DAPM list to avoid memory leak

Fix memory leak by releasing the dynamically allocated memory for
DAPM widget list in case of playback.

CRs-fixed: 386917
Change-Id: I6e79da9e5000c861dab6c15832e91f9fe0d5165d
Signed-off-by: Banajit Goswami <bgoswa@codeaurora.org>