mds : correction in the description for mds_log_max_segments config

Since we use unsigned integer for the config option
`mds_log_max_segments` , the value '-1' is not permitted.
And there's no need to disable this limit. Hence removing
this statement from the its description.

Fixes: https://tracker.ceph.com/issues/64064
Signed-off-by: Neeraj Pratap Singh <neesingh@redhat.com>