ASoC: msm8x16: fix the silence playback on enabling the sidetone path

In the current implementation the gain is muted while enabling
the interpolator and unmuted while enabling the DAC/PA.
If the sidetone is enabled the mixer controls enable the
DAPM sequence from the Tx to the IIR Rx path. After this when
the Rx path is powered up, only the interpolator is started
and not the end point(since it is already powered up by the IIR path).
This leads to the mute in the whole playback path.
Since there are no pops observed by removing the mute while
enabling the interpolator, hence removing the mute.

CRs-Fixed: 643806
Change-Id: I9d130363bab155a6240bb051a54bf6a6866e16c1
Signed-off-by: Aviral Gupta <aviralg@codeaurora.org>