ASoC: msm8x16-wcd: fix the pop during voice call disconnect

Powering down the sidetones path tears down the
interpolator clock along with it before the rx path is
teared down.
The change ensures that the interpolator clock will
tear down only when rx path is teared down.

Change-Id: I1144585bda1a489664ba08bed5478a5a332b9628
Signed-off-by: Aravind Kumar <akumark@codeaurora.org>