res_rtp_asterisk: Fix ssrc change for rtcp srtp

It looks like there was a copy/paste error in ast_rtp_change_source
where if there was a rtcp srtp instance, instead of updating its
ssrc we were updating the srtp instance ssrc twice.

ASTERISK-27022 #close
Reported-by: Michael Walton

Change-Id: Ic88f3aee7227b401c58745ac265ff92c19620095

res/res_rtp_asterisk.c

@@ -3447,7 +3447,7 @@ static void ast_rtp_change_source(struct ast_rtp_instance *instance)
 		ast_debug(3, "Changing ssrc for SRTP from %u to %u\n", rtp->ssrc, ssrc);
 		res_srtp->change_source(srtp, rtp->ssrc, ssrc);
 		if (rtcp_srtp != srtp) {
-			res_srtp->change_source(srtp, rtp->ssrc, ssrc);
+			res_srtp->change_source(rtcp_srtp, rtp->ssrc, ssrc);
 		}
 	}