ovl: fix getcwd() failure after unsuccessful rmdir

ovl: fix getcwd() failure after unsuccessful rmdir

ovl_remove_upper() should do d_drop() only after it successfully
removes the dir, otherwise a subsequent getcwd() system call will
fail, breaking userspace programs.

This is to fix: https://bugzilla.kernel.org/show_bug.cgi?id=110491

Signed-off-by: Rui Wang <rui.y.wang@intel.com>
Reviewed-by: Konstantin Khlebnikov <koct9i@gmail.com>
Signed-off-by: Miklos Szeredi <miklos@szeredi.hu>
Cc: <stable@vger.kernel.org>
Orabug: 24363418
CVE:CVE-2016-6198,CVE-2016-6197
Based on mainline v4.5 commit ce9113bbcbf45a57c082d6603b9a9f342be3ef74
Pre-req for mainline v4.6 commit 11f3710417d026ea2f4fcf362d866342c5274185
Conflicts:
  fs/overlayfs/dir.c - code base
Signed-off-by: Chuck Anderson <chuck.anderson@oracle.com>