cxgbei: Don't assert F for data completion PDUs.

If a data PDU encounters an error such as a digest error, the firmware
will report that data PDU when completion moderation is active even if
it is not the final data PDU in a burst.

Sponsored by: Chelsio Communications

(cherry picked from commit b5e73dd952f9d5224e9e076bb9719f7bcec871b0)