[SCSI] zfcp: Remove suspend callback

The callback for suspend is not required because it contains exactly
the same functionality as the _set_offline routine does.

Signed-off-by: Swen Schillig <swen@vnet.ibm.com>
Signed-off-by: Christof Schmitt <christof.schmitt@de.ibm.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>