[ftmod_misdn] Undefine MISDN_CONTROL_TYPE helper macro after use.

No reason to keep it around for longer.
Signed-off-by: Stefan Knoblich <stkn@openisdn.net>

libs/freetdm/src/ftmod/ftmod_misdn/ftmod_misdn.c

@@ -137,6 +137,7 @@ const static struct {
 } misdn_control_types[] = {
 #define MISDN_CONTROL_TYPE(x)	{ x, #x }
 	MISDN_CONTROL_TYPE(DTMF_HFC_COEF),
+#undef MISDN_CONTROL_TYPE
 };
 
 #if 0 /* unused for now */