futex: Always cleanup owner tid in unlock_pi

If the owner died bit is set at futex_unlock_pi, we currently do
not
cleanup the user space futex. So the owner TID of the current
owner
(the unlocker) persists. That's observable inconsistant
state,
especially when the ownership of the pi state got
transferred.

Clean it up unconditionally.

Signed-off-by: Thomas
Gleixner <tglx@linutronix.de>
Cc: Kees Cook <keescook@chromium.org>
Cc:
Will Drewry <wad@chromium.org>
Cc: Darren Hart
<dvhart@linux.intel.com>
Cc: stable@vger.kernel.org

Change-Id:
Ic84473a62bdf3e5702f46e04b266afa38e9ec40e

idea is taken here -
https://github.com/rmbq/android_kernel_htc_msm8960/commit/cc1035824fb9cfd75f9fdc2a182709d4e425c915