ASoC: wcd-mbhc: Fix detection of special headset

Comparison of headset threshold during special headset detection is
not proper. This results in to improper detection of special headset
and recording usecase failure on special headset. Fix the special
headset detection issue by adding proper check condition while selection
of headset threshold from device tree.

Change-Id: I4c338ded1bcb9fa643e1584eb23c6260fe52acee
Signed-off-by: Sudheer Papothi <spapothi@codeaurora.org>