btrfs: Extract duplicate decompress code

Add a common function to copy decompressed data from working buffer
to bio pages.

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>

diff --cc fs/btrfs/compression.c
Simple merge

diff --cc fs/btrfs/compression.h
Simple merge

diff --cc fs/btrfs/lzo.c
Simple merge

diff --cc fs/btrfs/zlib.c
Simple merge