Btrfs: csum_verify_file_block locking fix

Signed-off-by: Chris Mason <chris.mason@oracle.com>

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

diff --cc fs/btrfs/extent-tree.c
Simple merge

diff --cc fs/btrfs/file-item.c
Simple merge

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