f2fs: doc: fix wrong quota mount option description

We should use "{usr,grp,prj}jquota=" to disable journaled quota,
rather than using off{usr,grp,prj}jquota.

Fixes: 4b2414d0 ("f2fs: support journalled quota")
Signed-off-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>