dsp: adm: use default rate for unsupported sample rates

Some ECNS topologies can't support sample rate of 48KHZ,
reset it to 16KHZ for such use cases.

Change-Id: I5d0457feb2e74929546746fd4b184f2d7e065fbb
Signed-off-by: Yunfei Zhang <yunfeiz@codeaurora.org>