dsp: adm: change channel number for AUDIO_RX_MONO_VOIP module

AUDIO_RX_MONO_VOIP module in COPreP topology doesn't support
stereo input. Update channel number to mono for
AUDIO_RX_MONO_VOIP_COPP_TOPOLOGY.

Change-Id: I23632808cfcf82496f0e8f9618e28915974fc584
Signed-off-by: Kunlei Zhang <kunleiz@codeaurora.org>