scsi: ips: properly handle 64-bit DMA

CONFIG_HIGHMEM64 is only one (and these days unusual) way to indicate
that > 32-bit dma address are possible.  Replace it with a check of the
dma_addr_t size.

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