ahal: fix invalid pcm offload position when SSR happens

When SSR happens, postion queried from DSP could be invalid,
instead, frames written could be returned as current position.
Also cache the current position as compensation, when sound
card is online, return current DSP position plus the compensation.

Change-Id: Iff1b1ae9e5217f384d6ae0460b3acee5f8881aa5