schema compile CHANGE partial support for deviations

Currently supported deviations:
- not-supported
- add - units, must, default
- delete - units, must, default
- replace - units, default
diff --git a/src/tree_schema_free.c b/src/tree_schema_free.c
index aa026f7..559b635 100644
--- a/src/tree_schema_free.c
+++ b/src/tree_schema_free.c
@@ -491,7 +491,7 @@
     free(*w);
 }
 
-static void
+void
 lysc_must_free(struct ly_ctx *ctx, struct lysc_must *must)
 {
     lyxp_expr_free(ctx, must->cond);