update ffconf.h

components/dfs/filesystems/elmfat/ffconf.h

@@ -260,8 +260,11 @@
 /  Instead of private sector buffer eliminated from the file object, common sector
 /  buffer in the filesystem object (FATFS) is used for the file data transfer. */
 
-
-#define FF_FS_EXFAT		0
+#ifdef RT_DFS_ELM_USE_EXFAT
+#define FF_FS_EXFAT	1
+#else
+#define FF_FS_EXFAT	0
+#endif
 /* This option switches support for exFAT filesystem. (0:Disable or 1:Enable)
 /  To enable exFAT, also LFN needs to be enabled. (FF_USE_LFN >= 1)
 /  Note that enabling exFAT discards ANSI C (C89) compatibility. */