mgcp_sdp: correct apidoc of mgcp_parse_sdp_data

The API documentation of mgcp_parse_sdp_data is incorrect.

- correct API documentation

Change-Id: I9906f1dd6811c7092b93d60c9348221fef68cc3e
diff --git a/src/libosmo-mgcp/mgcp_sdp.c b/src/libosmo-mgcp/mgcp_sdp.c
index 52b4df4..5c66a83 100644
--- a/src/libosmo-mgcp/mgcp_sdp.c
+++ b/src/libosmo-mgcp/mgcp_sdp.c
@@ -205,10 +205,10 @@
  *  \param[in] endp trunk endpoint.
  *  \param[out] conn associated rtp connection.
  *  \param[out] caller provided memory to store the parsing results.
- *  \returns 0 on success, -1 on failure.
+ *  \returns 1 when codecs are assigned, 0 when no codecs are assigned.
  *
  *  Note: In conn (conn->end) the function returns the packet duration,
- *  the rtp port and the rtcp port */
+ *  rtp port, rtcp port and the assigned codecs (codec and alt_codec). */
 int mgcp_parse_sdp_data(const struct mgcp_endpoint *endp,
 			struct mgcp_conn_rtp *conn,
 			struct mgcp_parse_data *p)