rados: deprecated attribute has no argument

The deprecated attribute argument was introduced in gcc 4.5
http://gcc.gnu.org/gcc-4.5/changes.html and centos6 has a lower version.

Signed-off-by: Loic Dachary <loic@dachary.org>
Merge pull request #995 from dachary/wip-deprecated

rados: deprecated attribute has no argument