misc: Fix warnings about returning with value...

return rc in these cases.
diff --git a/openbsc/src/gsm_04_11.c b/openbsc/src/gsm_04_11.c
index f31e3f8..9b3f44e 100644
--- a/openbsc/src/gsm_04_11.c
+++ b/openbsc/src/gsm_04_11.c
@@ -678,6 +678,8 @@
 		trans->sms.cp_state = GSM411_CPS_IDLE;
 		trans_free(trans);
 	}
+
+	return rc;
 }
 
 static int gsm411_tx_cp_error(struct gsm_trans *trans, u_int8_t cause)