osd/osd_types.cc: prefer prefix ++operator for iterators

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>
osdc/Filer.cc: prefer prefix ++operator for iterators

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>
osdc/Filer.h: prefer prefix ++operator for iterators

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>
osdc/Objecter.h: prefer prefix ++operator for iterators

Prefer prefix ++operator for iterators, move one iterator declaration into
the for-loop header, since the iterator is only used within the loop.

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>