mpt3sas, mpt2sas: fix scsi_add_host error handling problems in _scsih_probe

In _scsih_probe, propagate the return value from scsi_add_host.
In mpt3sas, avoid calling list_del twice if that returns an
error, which causes list_del corruption warnings if an error
is returned.

Tested with blk-mq and scsi-mq patches to properly cleanup
from and propagate blk_mq_init_rq_map errors.

Signed-off-by: Robert Elliott <elliott@hp.com>
Acked-by: Sreekanth Reddy <Sreekanth.Reddy@avagotech.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>