btrfs: scrub: cleanup the argument list of scrub_chunk()
The argument list of scrub_chunk() has the following problems:
- Duplicated @chunk_offset
It is the same as btrfs_block_group::start.
- Confusing @length
The most instinctive guess is chunk length, and one may want to delete
it, but the truth is, it's the device extent length.
Fix this by:
- Remove @chunk_offset
Use btrfs_block_group::start instead.
- Rename @length to @dev_extent_len
Also rename the caller to remove the ambiguous naming.
- Rename @cache to @bg
The "_cache" suffix for btrfs_block_group has been removed for a while.
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>