nilfs2: remove loops of single statement macros

This fixes checkpatch.pl warning "WARNING: Single statement macros
should not use a do {} while (0) loop".

Link: http://lkml.kernel.org/r/1462886671-3521-7-git-send-email-konishi.ryusuke@lab.ntt.co.jp


Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>