reiserfs: Fix quota mount option parsing

When jqfmt mount option is not specified on remount, we mistakenly clear
s_jquota_fmt value stored in superblock. Fix the problem.

CC: stable@kernel.org
CC: reiserfs-devel@vger.kernel.org
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Nizar Lazuardy Firmansyah <nizar.digital@gmail.com>