Documentation: f2fs: Span write hint table section rows

Write hint policy table has two rows which act as section rows: buffered
io and direct io, yet these rows are written as normal rows instead.

Column-span them.

Signed-off-by: Bagas Sanjaya <bagasdotme@gmail.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

Author: bagasme

Documentation/filesystems/f2fs.rst

@@ -822,11 +822,13 @@ ioctl(COLD)           COLD_DATA                WRITE_LIFE_EXTREME
 extension list        "                        "
 
 -- buffered io
+------------------------------------------------------------------
 N/A                   COLD_DATA                WRITE_LIFE_EXTREME
 N/A                   HOT_DATA                 WRITE_LIFE_SHORT
 N/A                   WARM_DATA                WRITE_LIFE_NOT_SET
 
 -- direct io
+------------------------------------------------------------------
 WRITE_LIFE_EXTREME    COLD_DATA                WRITE_LIFE_EXTREME
 WRITE_LIFE_SHORT      HOT_DATA                 WRITE_LIFE_SHORT
 WRITE_LIFE_NOT_SET    WARM_DATA                WRITE_LIFE_NOT_SET