fsm.h: add missing include of logging.h

Change-Id: I783bf0eb40b674fb6a77f7673563fdf156975f5a
diff --git a/include/osmocom/core/fsm.h b/include/osmocom/core/fsm.h
index 269befa..7b262c7 100644
--- a/include/osmocom/core/fsm.h
+++ b/include/osmocom/core/fsm.h
@@ -10,6 +10,7 @@
 #include <osmocom/core/linuxlist.h>
 #include <osmocom/core/timer.h>
 #include <osmocom/core/utils.h>
+#include <osmocom/core/logging.h>
 
 /*! \defgroup fsm Finite State Machine abstraction
  *  @{