ext4: do not try to grab the s_umount semaphore in ext4_quota_off

It's not needed to sync the filesystem, and it fixes a lock_dep complaint.

Signed-off-by: Dmitry Monakhov <dmonakhov@gmail.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Reviewed-by: Jan Kara <jack@suse.cz>