[SCSI] zfcp: correctly initialize unchained requests

The common initialization of ct/gs and els requests missed the
initialization of unchained requests. Fix this by moving the common
parts to a place that is called for all ct/gs and els requests.

Reviewed-by: Felix Beck <felix.beck@de.ibm.com>
Signed-off-by: Christof Schmitt <christof.schmitt@de.ibm.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>