ext4: add a hint for block bitmap corrupt state in mb_groups

ext4: add a hint for block bitmap corrupt state in mb_groups

If one group is marked as block bitmap corrupted, its free blocks cannot
be used and its free count is also deducted from the global
sbi->s_freeclusters_counter. User might be confused about the absent
free space because we can't query the information about corrupted block
groups except unreliable error messages in syslog. So add a hint to show
block bitmap corrupted groups in mb_groups.

Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20240119061154.1525781-1-yi.zhang@huaweicloud.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>