scsi: megaraid_sas: set an unlimited max_segment_size

When using a virt_boundary_mask, as done for NVMe devices attached to
megaraid_sas controllers, we require an unlimited max_segment_size as the
virt boundary merging code assumes that.  But we also need to propagate
that to the DMA mapping layer to make dma-debug happy.  The SCSI layer
takes care of that when using the per-host virt_boundary setting, but
given that megaraid_sas only wants to set the virt_boundary for actual
NVMe devices, we can't rely on that.  The DMA layer maximum segment is
global to the HBA however, so we have to set it explicitly.  This patch
assumes that megaraid_sas does not have a segment size limitation, which
seems true based on the SGL format, but will need to be verified.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>