asoc: codecs: mbhc: Detect cross connection for mono headsets

Mono headsets have only one channel connected. Hence make cross
connection decision based on the voltage result of alteast one
channel showing cross connection.

Change-Id: I22a4ea7e25d09e785e7141f4a74c2830fdff555e
Signed-off-by: Ramprasad Katkam <katkam@codeaurora.org>