fat: Convert fat_fs_error to use %pV

- convert fat_fs_error to use %pV
- be consequent and use "supor_block *sb" instead of "supor_block *s"
- use devise name in each message.

Signed-off-by: Alexey Fisher <bug-track@fisher-privat.net>
Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>