[SCSI] zfcp: Reference counting for cfdc requests

Before dropping the reference count with zfcp_adapter_put, increase it
with zfcp_adapter_get when issuing cfdc requests.

Reviewed-by: Martin Petermann <martin@linux.vnet.ibm.com>
Signed-off-by: Christof Schmitt <christof.schmitt@de.ibm.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>