fat: fat16 support maximum 4GB file/vol size as WinXP or 7.

FAT16 support maximum 4GB vol/file size with 64KB cluster size.

Win NT/XP/7 increased the maximum cluster size to 64KB, and file/vol
size increased 4GB also.  Although increasing, the file size of linux
FAT is still limited at 2GB.

I found that it is limited by sb->maxbytes(0x7fffffff) when partition
is formatted by FAT16.  sb->s_maxbytes in fill_super should be set to
0xffffffff like fat32.

Signed-off-by: Namjae Jeon <linkinjeon@gmail.com>
Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>