fs/nilfs2: fix misspellings using codespell tool

Two typos are found out by codespell tool \
in 2217th and 2254th lines of segment.c:

$ codespell ./fs/nilfs2/
./segment.c:2217 :retured  ==> returned
./segment.c:2254: retured  ==> returned

Fix two typos found by codespell.

Link: https://lkml.kernel.org/r/1617864087-8198-1-git-send-email-konishi.ryusuke@gmail.com


Signed-off-by: Liu xuzhi <liu.xuzhi@zte.com.cn>
Signed-off-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>