isci: Code review change for completion pointer cleanup.

Since the request structure contains a pointer to the completion to be
used if the request is being aborted or terminated, there is no reason
to pass the completion as a pointer to isci_terminate_request_core().

Signed-off-by: Jeff Skirvin <jeffrey.d.skirvin@intel.com>
Signed-off-by: Jacek Danecki <Jacek.Danecki@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>