nilfs2: fix wrong accounting and duplicate brelse in nilfs_sufile_set_error

The nilfs_sufile_set_error() function wrongly adjusts the number of
dirty segments instead of the number of clean segments.  In addition,
the function calls brelse() twice for the same buffer head.

This fixes these bugs.

Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>