ASoC: msm: initiate mbhc_start only once

MBHC init is called twice due to which some of
the variables are re-initialised twice. Which is
leading to crash during stability tests with headset connected.

CRs-Fixed: 1080020
Change-Id: I48fddbcb846b578ceb39eadffdc067c798a48be6
Signed-off-by: Yeleswarapu Nagaradhesh <nagaradh@codeaurora.org>