futex: fix requeue_pi key imbalance

If futex_wait_requeue_pi() wakes prior to requeue, we drop the
reference to the source futex_key twice, once in
handle_early_requeue_pi_wakeup() and once on our way out.

Remove the drop from the handle_early_requeue_pi_wakeup() and keep
the get/drops together in futex_wait_requeue_pi().

Reported-by: Helge Bahmann <hcb@chaoticmind.net>
Signed-off-by: Darren Hart <dvhltc@us.ibm.com>
Cc: Helge Bahmann <hcb@chaoticmind.net>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Dinakar Guniguntala <dino@in.ibm.com>
Cc: John Stultz <johnstul@us.ibm.com>
Cc: stable-2.6.31 <stable@kernel.org>
LKML-Reference: <4ACCE21E.5030805@us.ibm.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>