ext4: let fiemap work with inline data

fiemap is used to find the disk layout of a file, as for inline data,
let us just pretend like a file with just one extent.

Signed-off-by: Tao Ma <boyu.mt@taobao.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

diff --cc fs/ext4/extents.c
Simple merge

diff --cc fs/ext4/inline.c
Simple merge

diff --cc fs/ext4/xattr.h
Simple merge