echo-cancel: Fix null implementation to setup one channel

memcpy() of the null implementation's run() copied data for only one
channel. Set the number of channels to 1 in init() in order to guarantee
this.

Signed-off-by: Stefan Huber <s.huber@bct-electronic.com>
Acked-by: Peter Meerwald <p.meerwald@bct-electronic.com>

src/modules/echo-cancel/null.c

@@ -32,6 +32,8 @@ pa_bool_t pa_null_ec_init(pa_core *c, pa_echo_canceller *ec,
     unsigned framelen = 256;
 
     source_ss->format = PA_SAMPLE_S16NE;
+    source_ss->channels = 1;
+
     *sink_ss = *source_ss;
     *sink_map = *source_map;