fix missing ringback silence calculation spot in switch_ivr_originate

src/switch_ivr_originate.c

@@ -1201,9 +1201,7 @@ static switch_status_t setup_ringback(originate_global_t *oglobals, originate_st
 					ringback->silence = atoi(c);
 				}
 			}
-			if (ringback->silence <= 0) {
-				ringback->silence = 400;
-			}
+			SWITCH_IVR_VERIFY_SILENCE_DIVISOR(ringback->silence);
 		} else {
 			switch_buffer_create_dynamic(&ringback->audio_buffer, 512, 1024, 0);
 			switch_buffer_set_loops(ringback->audio_buffer, -1);