ASoC: wcd9310/9304: Pull down Mic Bias output by default.

If Mic Bias is high Z by default and when the LDOH is enabled,
the Mic Bias output can pull-up to a non-zero voltage if there
is no loading or if the load leakage is very small.  Pulling
down the Mic Bias output so it is not in high Z to eliminate
the floating voltage.

Change-Id: I38e76a8c03107879727564f177b2713c9dfa4631
CRs-Fixed: 368898
Signed-off-by: Kuirong Wang <kuirongw@codeaurora.org>