ASoC: msm8226: modify fixup to update PCM format to 16 bit

Update fixup to set backend PCM format.This sets backend
tx format to be 16 bit pcm in case of tunnel mode playback

CRs-Fixed: 593469
Change-Id: Ia08c42bc2ed12f21355925438f605308268d6280
Signed-off-by: Yeleswarapu, Nagaradhesh <nagaradh@codeaurora.org>