metrics: equal operator should use ==
metrics: equal operator should use ==

A stupid copy and paste mistake, while changing the comparators in the
metric_id.

Signed-off-by: Amnon Heiman <ed5fc74c4692051ad0b19749fd7cea6ec2d74b9e@scylladb.com>
Message-Id: <1485087517-12832-1-git-send-email-ed5fc74c4692051ad0b19749fd7cea6ec2d74b9e@scylladb.com>

cloudius-systems/seastar,syuu1228/seastar,dreamsxin/seastar,scylladb/seastar,syuu1228/seastar,cloudius-systems/seastar,avikivity/seastar,avikivity/seastar,scylladb/seastar,syuu1228/seastar,avikivity/seastar,dreamsxin/seastar,scylladb/seastar,dreamsxin/seastar,cloudius-systems/seastar