futex: fix restart for early wakeup in futex_wait_requeue_pi()

The futex_wait_requeue_pi op should restart unconditionally like
futex_lock_pi. The user of that function e.g. pthread_cond_wait can
not be interrupted so we do not care about the SA_RESTART flag of the
signal. Clean up the FIXMEs.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>