osd: silence warnings from -Wsign-compare

osd: silence warnings from -Wsign-compare

Fixed the warning :

ceph/src/osd/OSDMap.cc: In member function ‘int OSDMap::validate_crush_rules(CrushWrapper*, std::ostream*) const’:
ceph/src/osd/OSDMap.cc:3278:25: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     if (pool.get_size() < (int)newcrush->get_rule_mask_min_size(ruleno) ||
         ~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
ceph/src/osd/OSDMap.cc:3279:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  pool.get_size() > (int)newcrush->get_rule_mask_max_size(ruleno)) {
  ~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Signed-off-by: Jos Collin <jcollin@redhat.com>