osd/PG: fix choose_acting revert to up case

If we decide to revert back to up, we need to

1- return false, so that we go into the NeedActingChange state, and 2-
actually ask for that change.

It's too fugly to try to jump down to the existing queue_want_pg_temp call
100+ lines down in this function, so just do it here.  We already know that
we are requesting to clear the pg_temp.

Fixes: #7902 Backport: emperor, dumpling Signed-off-by: Sage Weil
<sage@inktank.com>