[SCSI] scsi_lib_dma: fix bug with dma maps on nested scsi objects

Some of our virtual SCSI hosts don't have a proper bus parent at the
top, which can be a problem for doing DMA on them

This patch makes the host device cache a pointer to the physical bus
device and provides an extra API for setting it (the normal API picks
it up from the parent).  This patch also modifies the qla2xxx and lpfc
vport logic to use the new DMA host setting API.

Acked-By: James Smart <james.smart@emulex.com>
Cc: Stable Tree <stable@kernel.org>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>