Correct panics with eh_timeout and eh_deadline

We were having double completions on our SLI-3 version of adapters.
Solved by clearing our command pointer before calling scsi_done.

The eh paths potentially ran simulatenously and would see the non-null
value and invoke scsi_done again.
Signed-off-by: NDick Kennedy <dick.kennedy@broadcom.com>
Signed-off-by: NJames Smart <james.smart@broadcom.com>
Reviewed-by: NJohannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: NHannes Reinecke <hare@suse.com>
Signed-off-by: NMartin K. Petersen <martin.petersen@oracle.com>