asoc: update number of channel only for default channel map

Volume setting on the custom channel map is failed as
use default channel map is always set to true.
Use default channel map from runtime data and update
number of channels only if custom channel map is not set.

Change-Id: I2326b52687144a584f85ab3db8a2930f8fa5c3ea
Signed-off-by: Surendar Karka <skarka@codeaurora.org>