examples: Fix warnings of key_value_test.
examples: Fix warnings of key_value_test.

jhrozek/cmocka,dsch/cmocka,jamesmunns/CMocka,jhrozek/cmocka,VladimirTyrin/cmocka,nuumio/cmocka,tyc/cmocka,jamesmunns/CMocka,clibs/cmocka,aleksandr-vin/cmock,jschmidlapp/cmocka,jschmidlapp/cmocka,wingyplus/cmocka,Odie/cmocka,linuxmaniac/cmocka,aleksandr-vin/cmock,VladimirTyrin/cmocka,nuumio/cmocka,wingyplus/cmocka,chadversary/cmocka,JonathonReinhart/cmocka,Odie/cmocka,chadversary/cmocka,JonathonReinhart/cmocka,lsjostro/cmocka,jhrozek/cmocka,Odie/cmocka,linuxmaniac/cmocka,nuumio/cmocka,akikoskinen/cmocka,tyc/cmocka,clibs/cmocka,dsch/cmocka,tyc/cmocka,lsjostro/cmocka,jschmidlapp/cmocka