Bug 688341 - (cov#10702) Fix Coverity code maintainability issues

We are computing the size of memory needed by using the incorrect
pointer type.

ldap/servers/slapd/mapping_tree.c

@@ -1535,7 +1535,7 @@ add_internal_mapping_tree_node(const char *subtree, Slapi_Backend *be, mapping_t
 {
     Slapi_DN *dn;
     mapping_tree_node *node;
-    backend ** be_list = (backend **) slapi_ch_malloc(sizeof(backend **));
+    backend ** be_list = (backend **) slapi_ch_malloc(sizeof(backend *));
 
     be_list[0] = be;