ocfs2: rollback the cleared bits if error occurs after ocfs2_block_group_clear_bits

ocfs2_block_group_clear_bits will clear bits in block group bitmap.
Once it succeeds but fails in the following step, it will cause block
group bitmap mismatch the corresponding count recorded in dinode.
So rollback the cleared bits if error occurs.

Signed-off-by: Joseph Qi <joseph.qi@huawei.com>
Cc: Mark Fasheh <mfasheh@suse.com>
Cc: Joel Becker <jlbec@evilplan.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>