LU-1069 mdc: Avoid doing permission check again.

LU-1069 mdc: Avoid doing permission check again.

inode_setattr() replaced by simple_setattr(). The latter
will invoke inode_change_ok(). It causes a -EPERM error when
we want to update inode timestamps.

Signed-off-by: yang sheng <ys@whamcloud.com>
Change-Id: I29c58d7027df1bf94db58df82e5214fd12ea5c87
Reviewed-on: http://review.whamcloud.com/2145
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Fan Yong <yong.fan@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>