plugins exts BUGFIX storage must be 8B large

Fixes #2253
diff --git a/src/tree_schema_internal.h b/src/tree_schema_internal.h
index fecccf5..d3e399c 100644
--- a/src/tree_schema_internal.h
+++ b/src/tree_schema_internal.h
@@ -730,7 +730,7 @@
  * @return LY_SUCCESS on success.
  * @return LY_ENOT if the substatement is not supported.
  */
-LY_ERR lyplg_ext_get_storage_p(const struct lysc_ext_instance *ext, int stmt, const void ***storage_p);
+LY_ERR lyplg_ext_get_storage_p(const struct lysc_ext_instance *ext, int stmt, uint64_t *storage_p);
 
 /**
  * @brief Warning if the filename does not match the expected module name and version