mgcp_client_fsm: add missing log_subsys

To see state transitions and events on LMGCP DEBUG logging, actually set
the log_subsys of the mgcp_client_fsm.

Related: SYS#5529
Change-Id: I6e84d5f7b85752a7a54f17be1d074b01d1467f26
diff --git a/src/libosmo-mgcp-client/mgcp_client_fsm.c b/src/libosmo-mgcp-client/mgcp_client_fsm.c
index 57c6d98..3f33dc7 100644
--- a/src/libosmo-mgcp-client/mgcp_client_fsm.c
+++ b/src/libosmo-mgcp-client/mgcp_client_fsm.c
@@ -596,6 +596,7 @@
 	.timer_cb = fsm_timeout_cb,
 	.cleanup = fsm_cleanup_cb,
 	.event_names = fsm_mgcp_client_evt_names,
+	.log_subsys = DLMGCP,
 };
 
 /*! allocate FSM, and create a new connection on the MGW.