hal: correct frames_read implementation.

dsp_latency have to be populated from platform_info
xml and it is only used by one PL.
Fix the hardcoded constant value and return 0 for
dsp_latency for normal PLs.
Having constant value subtracting from frames_read
results in av sync issues and fix the same.

Change-Id: I87d1da95f16c5266662bc2f45ed926308cb302f5