[SCSI] zfcp: Zero memory for gpn_ft and adisc requests

With debug kernels, the memory allocated with kmem_cache_alloc might
be initialized with the poison values 6b and a5. Use kmem_cache_zalloc
instead of kmem_cache_alloc to get zeroed memory and not send invalid
requests.

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