reiserfs: Fix memory leak in reiserfs_parse_options()

When a usrjquota or grpjquota mount option is used multiple times, we
will leak memory allocated for the file name. Make sure the last setting
is used and all the previous ones are properly freed.

Reported-by:  <syzbot+c9e294bbe0333a6b7640@syzkaller.appspotmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>