futex: Deduplicate cond_resched() invocation in futex_wake_op()

After pagefaulting in futex_wake_op() both branches do cond_resched()
before retry. Deduplicate it as compilers cannot figure it out themself.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Davidlohr Bueso <dbueso@suse.de>
Link: https://lore.kernel.org/r/9b2588c1fd33c91fb01c4e348a3b647ab2c8baab.1621258128.git.asml.silence@gmail.com