plugins exts BUGFIX storage must be 8B large

Fixes #2253
diff --git a/src/tree_schema_free.c b/src/tree_schema_free.c
index 10b1c6c..145ae8f 100644
--- a/src/tree_schema_free.c
+++ b/src/tree_schema_free.c
@@ -1520,7 +1520,7 @@
 
         case LY_STMT_TYPE: {
             /* single type */
-            struct lysp_type **type_p = substmts[u].storage;
+            struct lysp_type **type_p = (void *)substmts[u].storage;
 
             lysp_type_free(&fctx, *type_p);
             free(*type_p);
@@ -1635,7 +1635,7 @@
         }
         case LY_STMT_WHEN:
             /* single item, expects a pointer */
-            lysc_when_free(&fctx, substmts[u].storage);
+            lysc_when_free(&fctx, (struct lysc_when **)substmts[u].storage);
             break;
 
         case LY_STMT_PATTERN: {