json2cbor: Minor update for clarity

Avoids a magic constant in the code.

Signed-off-by: Thiago Macieira <thiago.macieira@intel.com>
diff --git a/tools/json2cbor/json2cbor.c b/tools/json2cbor/json2cbor.c
index a49d6af..3754a1a 100644
--- a/tools/json2cbor/json2cbor.c
+++ b/tools/json2cbor/json2cbor.c
@@ -365,7 +365,7 @@
 
         for (item = json->child ; item; item = item->next) {
             if (usingMetaData && strlen(item->string) > strlen(meta_data_marker)
-                    && strcmp(item->string + strlen(item->string) - 5, meta_data_marker) == 0)
+                    && strcmp(item->string + strlen(item->string) - strlen(meta_data_marker), meta_data_marker) == 0)
                 continue;
 
             err = cbor_encode_text_stringz(&container, item->string);