scsi: sas: provide stub implementation for scsi_is_sas_rphy

Provide a stub implementation for scsi_is_sas_rphy for kernel
configurations which do not have CONFIG_SCSI_SAS_ATTRS defined.

Reported-by: kbuild test robot <lkp@intel.com>
Suggested-by: James Bottomley <jejb@linux.vnet.ibm.com>
Reviewed-by: James E.J. Bottomley <jejb@linux.vnet.ibm.com>
Signed-off-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>