atomic: fix atomic_cas* comment documenting the behavior
atomic: fix atomic_cas* comment documenting the behavior

It was backwards from reality (and tests).  Returning the "before" value is
more useful because it allows us to retry the CAS without having to reload
the variable to get the old value.

Signed-off-by: Josef 'Jeff' Sipek <a620f141433c70aa9e43778305a6c68cbfadfb25@josefsipek.net>

jeffpc/libjeffpc,jeffpc/libjeffpc,jeffpc/libjeffpc,jeffpc/libjeffpc