cql3: statements: create_service_level_statement: don't ignore replace_defaults()
cql3: statements: create_service_level_statement: don't ignore replace_defaults()

We call replace_defaults on an object named 'slo', but then ignore it.

Use the new object that replace_defaults() returned.

Reported by gcc 11.

scylladb/scylla,scylladb/scylla,scylladb/scylla,scylladb/scylla