Use default sample rate for DIRECT Audio thread

DIRECT and OFFLOAD Audio threads use the mixer when using SW effects.
This requires them to use the default sample rate.

Test: vendor specific, see bug
Bug: 147209612
Merged-In: I553fe43695d64160dd64808e18299699a4047225
Change-Id: I553fe43695d64160dd64808e18299699a4047225