ASoC: wcd9xxx: Do not acquire codec resource lock to get hph impedance

Acquiring codec resource lock within get impedance function may
cause deadlock when headset inserted/removed repeatedly. Remove
the lock as it is not required to be protected with a mutex.

CRs-fixed: 597226
Change-Id: I20865e0b2bb193f2f8777f2b69e735a0d4997cca
Signed-off-by: Phani Kumar Uppalapati <phaniu@codeaurora.org>