Summary:
- Due to the recent changes of wchar_t, ls command always
causes errors for the fat file system.
- This commit fixes this issue by replacing wchar_t with
uint16_t under fs/fat
Impact:
- None
Testing:
- Tested with spresense:wifi and stm32f4discovery:wifi
Signed-off-by: Masayuki Ishikawa <Masayuki.Ishikawa@jp.sony.com>