isp: fix ISPCTL_ABORT_CMD switch case

Prevent kernel panic by not running ISPCTL_FCLINK_TEST after a
failed ISPCTL_ABORT_CMD.

Reviewed by: mav
Tested by: Arne Steinkamm <arne@steinkamm.com>
MFC after: 3 days
Differential Revision: https://reviews.freebsd.org/D45718