ocfs2: replace BUG_ON() at ocfs2_num_free_extents() with ocfs2_error()

ocfs2: replace BUG_ON() at ocfs2_num_free_extents() with ocfs2_error()

The BUG_ON() at ocfs2_num_free_extents() handles the error that
l_tree_deepth of leaf extent block just read form disk is invalid.  This
error is mostly caused by file system metadata corruption on the disk.
There is no need to call BUG_ON() to handle such errors.  We can return
error code, since the caller can deal with errors from
ocfs2_num_free_extents().  Also, we should make the file system read-only
to avoid the damage from expanding.

Therefore, BUG_ON() is removed and ocfs2_error() is called instead.

Link: https://lkml.kernel.org/r/20231018191811.412458-1-jindui71@gmail.com
Signed-off-by: Jia Rui <jindui71@gmail.com>
Reviewed-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>