ASoC: wcd9xxx: Reset flyback current for TASHA_2_0

Impedance calculation of HPH_L and HPH_R are affected
on targets with TASHA_2_0 due to flyback current.
Set flyback current to 0 for HPH before impedance calculation.

Change-Id: I4f2387e5ae67d3fabbd5b7f14756bf75d79ba0d0
Signed-off-by: Soumya Managoli <smanag@codeaurora.org>