mpt3sas: avoid mpt3sas_transport_port_add NULL parent_dev

If _scsih_sas_host_add's call to mpt3sas_config_get_sas_iounit_pg0
fails, ioc->sas_hba.parent_dev may be left uninitialized.  A later
device probe could invoke mpt3sas_transport_port_add which will call
sas_port_alloc_num [scsi_transport_sas] with a NULL parent_dev pointer.

Signed-off-by: Joe Lawrence <joe.lawrence@stratus.com>
Acked-by: Sreekanth Reddy <sreekanth.reddy@broadcom.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>