reiserfs: Fix quota mount option parsing

commit a06d789b upstream.

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

CC: reiserfs-devel@vger.kernel.org
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>