locking/osq_lock: Clarify osq_wait_next()

Directly return NULL or 'next' instead of breaking out of the loop.

Signed-off-by: David Laight <david.laight@aculab.com>
[ Split original patch into two independent parts  - Linus ]
Link: https://lore.kernel.org/lkml/7c8828aec72e42eeb841ca0ee3397e9a@AcuMS.aculab.com/


Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>