AudioPolicy: only hotword active fails when echo reference is active

Preconditions:
-echo reference source is available
-Google assistant is listening to hotword (and recording echo ref as
well).
-Another assistant is set as active and is also listening to hotword
(recording echo ref as well).

Google assistant is recording silence when Other assistant is on TOP.

This CL fixes by filtering out virtual sources to detect hotword only
case.

Bug: 254300623

Signed-off-by: François Gaffie <francois.gaffie@renault.com>
Change-Id: I04b2600e00c57fe0e00a793b2edd1b810f5ee2e2