LU-484 Don't do error cleanup in ext4_add_dot_dotdot()

LU-484 Don't do error cleanup in ext4_add_dot_dotdot()

The ext4_add_dot_dotdot() will do cleanup work (zeroing i_nlink, iput)
when ext4_bread() fails, that will mess up the i_nlink and i_count if
the ext4_add_dot_dotdot() is called from lustre.

The error cleanup work should be moved from ext4_add_dot_dotdot() to
it's caller: ext4_mkdir().

Signed-off-by: Niu Yawei <niu@whamcloud.com>
Change-Id: I8e8a328c26bf5d603ca26c94a5a04cf8bd1c7b4f
Reviewed-on: http://review.whamcloud.com/1079
Tested-by: Hudson
Reviewed-by: Johann Lombardi <johann@whamcloud.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>