nilfs2: remove the unneeded result variable

Return the value nilfs_segctor_sync() directly instead of storing it in
another redundant variable.

Link: https://lkml.kernel.org/r/20220831033403.302184-1-ye.xingchen@zte.com.cn
Link: https://lkml.kernel.org/r/20220921034803.2476-3-konishi.ryusuke@gmail.com
Reported-by: Zeal Robot <zealci@zte.com.cn>
Signed-off-by: ye xingchen <ye.xingchen@zte.com.cn>
Signed-off-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Cc: Minghao Chi <chi.minghao@zte.com.cn>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>