scsi: ibmvscsis: Fix a stringop-overflow warning

There's currently a warning about string overflow with strncat:

drivers/scsi/ibmvscsi_tgt/ibmvscsi_tgt.c: In function 'ibmvscsis_probe':
drivers/scsi/ibmvscsi_tgt/ibmvscsi_tgt.c:3479:2: error: 'strncat' specified
bound 64 equals destination size [-Werror=stringop-overflow=]
  strncat(vscsi->eye, vdev->name, MAX_EYE);
  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Switch to a single snprintf instead of a strcpy + strcat to handle this
cleanly.

Signed-off-by: Laura Abbott <labbott@redhat.com>
Suggested-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>