ntfs: repair docum. malformed table

ntfs: repair docum. malformed table

Make the top and bottom borders be that same length to
avoid a documentation build error:

Documentation/filesystems/ntfs.rst:159: ERROR: Malformed table.
Bottom border or header rule does not match top border.

(top)
======================= ===================================================
(bottom)
======================= ==================================================

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Reviewed-by: Hyunchul Lee <hyc.lee@gmail.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>