Btrfs: get rid of sparse warnings

make C=2 fs/btrfs/ CF=-D__CHECK_ENDIAN__

I tried to filter out the warnings for which patches have already
been sent to the mailing list, pending for inclusion in btrfs-next.

All these changes should be obviously safe.

Signed-off-by: Stefan Behrens <sbehrens@giantdisaster.de>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>
Signed-off-by: Chris Mason <chris.mason@fusionio.com>

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

diff --cc fs/btrfs/check-integrity.c
Simple merge

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

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

diff --cc fs/btrfs/delayed-ref.c
Simple merge

diff --cc fs/btrfs/disk-io.c
Simple merge

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

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

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