ftmod_libpri: Fix type-punned pointer warning in msn_filter_foreach().

cc1: warnings being treated as errors
./src/ftmod/ftmod_libpri/ftmod_libpri.c: In function 'msn_filter_foreach':
./src/ftmod/ftmod_libpri/ftmod_libpri.c:422: warning: dereferencing type-punned pointer will break strict-aliasing rules
make: *** [ftmod_libpri_la-ftmod_libpri.lo] Error 1
Signed-off-by: Stefan Knoblich <stkn@openisdn.net>

libs/freetdm/src/ftmod/ftmod_libpri/ftmod_libpri.c

@@ -417,11 +417,11 @@ static int msn_filter_foreach(ftdm_libpri_data_t *isdn_data, int (* func)(const
 	ftdm_mutex_lock(isdn_data->msn_mutex);
 
 	for (iter = hashtable_first(isdn_data->msn_hash); iter; iter = hashtable_next(iter)) {
-		const char *msn = NULL;
+		const void *msn = NULL;
 
-		hashtable_this(iter, (const void **)&msn, NULL, NULL);
+		hashtable_this(iter, &msn, NULL, NULL);
 
-		if (ftdm_strlen_zero(msn))
+		if (ftdm_strlen_zero((const char *)msn))
 			break;
 		if ((ret = func(msn, data)) != FTDM_SUCCESS)
 			break;