ASoC: rouleur-mbhc: Fix impedance detection issue on rouleur

Impedance values are not correct sometimes due to ramp
being controlled by hw. Run detection routine for sometime
and take final value as impedance value to resolve issue.

Change-Id: I3a34813657751aa304e150cfa294a42f556d06c4
Signed-off-by: Vatsal Bucha <vbucha@codeaurora.org>