crush: adjust local retry threshold

This small adjustment reflects a change that was made in ceph.git commit
af6a9f30696c900a2a8bd7ae24e8ed15fb4964bb, about 6 months ago.  An N-1
search is not exhaustive.  Fixed ceph.git bug #1594.

Reviewed-by: Alex Elder <elder@inktank.com>
Signed-off-by: Sage Weil <sage@inktank.com>