dsp: adm: change channel number for SMECNS_V2 module

SMECNS_V2 module in COPreP topology doesn't support
stereo input. Update channel number to mono for
VPM_TX_VOICE_SMECNS_V2_COPP_TOPOLOGY, which contains
SMECNS_V2 module.

Change-Id: I04b971b41328f6a32bf0ff42b21496b49bb4140b
Signed-off-by: Kunlei Zhang <kunleiz@codeaurora.org>