common: JSON output from rados bench write has typo in max_latency key
The JSON output from `rados bench write --format json/json-pretty` has a typo in the `max_latency` key.
It contains an colon after the key name, "max_latency:"
Only applies for `rados bench write`.
Introduced in v9.1.0 in https://github.com/ceph/ceph/commit/08296dc0febc4ee3b1c5f860d8744bd04e9c2ff8.
Offending line in https://github.com/ceph/ceph/commit/08296dc0febc4ee3b1c5f860d8744bd04e9c2ff8#diff-77d6052552f1e1330c1d4fbf33702764R546.