asoc: lpass-cdc: fix the channel count logic in Tx macro

Change for not increasing the active_channel_count value if the mixer
control corresponding to the Dec is already set.

Change-Id: Iad2e513f16bbe2768ff302f72bd9a5af31042b4b
Signed-off-by: Pratyush Meduri <quic_mpratyus@quicinc.com>