[SCSI] zfcp: Remove ZFCP_SYSFS_FAILED macro and implement fcp_lun_show without macro

These sysfs attributes will require different functions. Implement
them without using macros, so that the open coded functions can be
changed later.

Reviewed-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>