oofatfs: Set API encoding to UTF-8

Since micropython uses a utf-8 string encoding, the FAT long file names
(represented as UCS-2 on disk) should be encoded as UTF-8 on the API.

This fixes the problem that files on VFAT that have umlauts in their
file names are not shown correctly on the micropython side.

Signed-off-by: Matthias Blankertz <matthias@blankertz.org>

lib/oofatfs/ffconf.h

@@ -164,7 +164,7 @@
 /  ff_memfree() in ffsystem.c, need to be added to the project. */
 
 
-#define FF_LFN_UNICODE  0
+#define FF_LFN_UNICODE  2
 /* This option switches the character encoding on the API when LFN is enabled.
 /
 /   0: ANSI/OEM in current CP (TCHAR = char)