update source/ff.c.

source/ff.c

@@ -1980,7 +1980,7 @@ DWORD dir_ofs (
 #if FF_USE_LFN
 	UINT nlen, nent;
 	DWORD entry;
-	for (nlen = 0; fs->lfnbuf[nlen]; nlen++) ;	/* Get lfn length */
+	for (nlen = 0; dp->obj.fs->lfnbuf[nlen]; nlen++) ;	/* Get lfn length */
 	nent = (dp->fn[NSFLAG] & NS_LFN) ? (nlen + 12) / 13 + 1 : 1;	/* Number of entries of the lfn */
 	entry = dp->dptr - (nent - 1) * SZDIRE;
 	return entry;