Clean up reference to AEN command if abort AEN is succesful as the command is aborted.
Did the same by setting sc->aen_cmd = NULL when aborting AEN is successful.

Submitted by: Sumit Saxena <sumit.saxena@broadcom.com>
Reviewed by: Kashyap Desai <Kashyap.Desai@broadcom.com>
MFC after: 3 days
Sponsored by: Broadcom Limited/AVAGO Technologies