cls_kvs.cc: remove dead assignment

Fix for:
[src/key_value_store/cls_kvs.cc:383] -> [src/key_value_store/cls_kvs.cc:386]:
 (performance) Variable 'r' is reassigned a value before the old one has been used.

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