After the data is written successfully, we should cleanup the read failure record
in that range because
- If we set data COW for the file, the range that the failure record pointed to is
  mapped to a new place, so it is invalid.
- If we set no data COW for the file, and if there is no error during writting,
  the corrupted data is corrected, so the failure record can be removed. And if
  some errors happen on the mirrors, we also needn't worry about it because the
  failure record will be recreated if we read the same place again.

Sometimes, we may fail to correct the data, so the failure records will be left
in the tree, we need free them when we free the inode or the memory leak happens.
Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
Signed-off-by: Chris Mason <clm@fb.com>