fs/fat: use fat_msg() to replace printk() in __fat_fs_error()

Signed-off-by: Gu Zheng <guz.fnst@cn.fujitsu.com>
Acked-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>