Fix Version/s: None
As discussed on Slack: https://lsstc.slack.com/archives/CBE964PR8/p1552065738002400
ccdExposureId_bits has been set to 38 for both imSim and phoSim on branch:
DESC will need this fix in place for DC2 Run2.1i data processing.
I will make a ticket branch and issue a PR.