libeffects: Fix for crash during playback on bluetooth headset

Crash was because of uninitialized (invalid) number of channels.
Initialized channels to default value and ensured
that during set config channel and channel mask value
are updated per the input config.

Test: BT playback with Spotify, GPM (Sailfish)
Bug: 129804987
Bug: 130013184
Change-Id: I71069b13a90e02bfc3b5cb9bf69c4c65c10ae36f