comment out unused variable to satisfy build when compiling under core CFLAGS with warnings as errors

libs/spandsp/src/plc.c

@@ -165,10 +165,10 @@ SPAN_DECLARE(int) plc_fillin(plc_state_t *s, int16_t amp[], int len)
     float old_weight;
     float new_weight;
     float gain;
-    int16_t *orig_amp;
+    //int16_t *orig_amp;
     int orig_len;
 
-    orig_amp = amp;
+    //orig_amp = amp;
     orig_len = len;
     if (s->missing_samples == 0)
     {