scsi: isci: Change sci_controller_start_task's return type to sci_status

Clang warns when an enumerated type is implicitly converted to another.

drivers/scsi/isci/request.c:3476:13: warning: implicit conversion from
enumeration type 'enum sci_task_status' to different enumeration type
'enum sci_status' [-Wenum-conversion]
                        status = sci_controller_start_task(ihost,
                               ~ ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/scsi/isci/host.c:2744:10: warning: implicit conversion from
enumeration type 'enum sci_status' to different enumeration type 'enum
sci_task_status' [-Wenum-conversion]
                return SCI_SUCCESS;
                ~~~~~~ ^~~~~~~~~~~
drivers/scsi/isci/host.c:2753:9: warning: implicit conversion from
enumeration type 'enum sci_status' to different enumeration type 'enum
sci_task_status' [-Wenum-conversion]
        return status;
        ~~~~~~ ^~~~~~

Avoid all of these implicit conversion by just making
sci_controller_start_task use sci_status. This silences
Clang and has no functional change since sci_task_status
has all of its values mapped to something in sci_status.

Link: https://github.com/ClangBuiltLinux/linux/issues/153


Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>