btrfs: pass a btrfs_bio to btrfs_submit_compressed_read

btrfs_submit_compressed_read expects the bio passed to it to be embedded
into a btrfs_bio structure.  Pass the btrfs_bio directly to increase type
safety and make the code self-documenting.

Reviewed-by: Anand Jain <anand.jain@oracle.com>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: David Sterba <dsterba@suse.com>