btrfs: btrfs_decompress_bio() could accept compressed_bio instead

Instead of sending each argument of struct compressed_bio, send
the compressed_bio itself.

Also by having struct compressed_bio in btrfs_decompress_bio()
it would help tracing.

Signed-off-by: Anand Jain <anand.jain@oracle.com>
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>