ext4: Always set dx_node's fake_dirent explicitly.

ext4: Always set dx_node's fake_dirent explicitly.

(cherry picked from commit 1f7bebb9e911d870fa8f997ddff838e82b5715ea)

When ext4_dx_add_entry() has to split an index node, it has to ensure that
name_len of dx_node's fake_dirent is also zero, because otherwise e2fsck
won't recognise it as an intermediate htree node and consider the htree to
be corrupted.

Signed-off-by: Andreas Schlick <schlick@lavabit.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>