scsi: mpt3sas: clarify mmio pointer types

The newly added code mixes up phys_addr_t/resource_size_t with dma_addr_t
and void pointers, as seen from these compiler warning:

drivers/scsi/mpt3sas/mpt3sas_base.c: In function '_base_get_chain_phys':
drivers/scsi/mpt3sas/mpt3sas_base.c:235:21: error: cast to pointer from integer of different size [-Werror=int-to-pointer-cast]
  base_chain_phys  = (void *)ioc->chip_phys + MPI_FRAME_START_OFFSET +
                     ^
drivers/scsi/mpt3sas/mpt3sas_base.c: In function '_clone_sg_entries':
drivers/scsi/mpt3sas/mpt3sas_base.c:427:20: error: cast from pointer to integer of different size [-Werror=pointer-to-int-cast]
    sgel->Address = (dma_addr_t)dst_addr_phys;
                    ^
drivers/scsi/mpt3sas/mpt3sas_base.c:438:7: error: cast from pointer to integer of different size [-Werror=pointer-to-int-cast]
       (dma_addr_t)buff_ptr_phys;
       ^
drivers/scsi/mpt3sas/mpt3sas_base.c:444:10: error: cast from pointer to integer of different size [-Werror=pointer-to-int-cast]
          (dma_addr_t)buff_ptr_phys;

Both dma_addr_t and phys_addr_t may be wider than a pointer, so we must
avoid the conversion to pointer types. This also helps readability.

A second problem is treating MMIO addresses from a 'struct resource'
as addresses that can be used for DMA on that device. In almost all
cases, those are the same, but on some of the more obscure architectures,
PCI memory address 0 is mapped into the CPU address space at a nonzero
offset. I don't have a good fix for that, so I'm adding a comment here,
plus a WARN_ON() that triggers whenever the phys_addr_t number is
outside of the low 32-bit address space and causes a straight overflow
when assigned to the 32-bit sgel->Address.

Fixes: 182ac784 ("scsi: mpt3sas: Introduce Base function for cloning.")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Sreekanth Reddy <Sreekanth.Reddy@broadcom.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>