fat: fix return value of vfat_bad_char() and vfat_replace_char() functions

These functions returns boolean value not wide character.

Link: https://lkml.kernel.org/r/20221226142512.13848-1-pali@kernel.org


Signed-off-by: Pali Rohár <pali@kernel.org>
Acked-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>