osd: Optimized EC don't try to trim past crt

osd: Optimized EC don't try to trim past crt

If there is an exceptionally long sequence of partial writes
that did not update a shard that is followed by a full write
then it is possible that the log trim point is ahead of the
previous write to the shard (and hence crt). We cannot trim
beyond crt. In this scenario its fine to limit the trim to crt
because the shard doesn't have any of the log entries for the
partial writes so there is nothing more to trim.

Signed-off-by: Bill Scales <bill_scales@uk.ibm.com>
(cherry picked from commit 645cdf9f61e79764eca019f58a4d9c6b51768c81)