ocfs2: use BUG_ON instead of if condition followed by BUG.

This issue was detected with the help of Coccinelle.

Link: https://lkml.kernel.org/r/20211105014424.75372-1-zhang.mingyu@zte.com.cn
Signed-off-by: Zhang Mingyu <zhang.mingyu@zte.com.cn>
Reported-by: Zeal Robot <zealci@zte.com.cn>
Acked-by: Joseph Qi <joseph.qi@linux.alibaba.com>
Cc: Mark Fasheh <mark@fasheh.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Junxiao Bi <junxiao.bi@oracle.com>
Cc: Changwei Ge <gechangwei@live.cn>
Cc: Gang He <ghe@suse.com>
Cc: Jun Piao <piaojun@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>