Doxygen: fix incorrect / missing parameter description

Change-Id: Ibc63a5d4442a192efab8b5b30e0beb3545642ecc
diff --git a/src/fsm.c b/src/fsm.c
index 5723bab..d86ff4b 100644
--- a/src/fsm.c
+++ b/src/fsm.c
@@ -395,7 +395,7 @@
 }
 
 /*! delete a given instance of a FSM
- *  \param[in] fsm The FSM to be un-registered and deleted
+ *  \param[in] fi FSM instance to be un-registered and deleted
  */
 void osmo_fsm_inst_free(struct osmo_fsm_inst *fi)
 {