The code that prepares the SG associated with SCSI command for FMR was
buggy for systems with DMA addresses that don't fit in unsigned long,
e.g under the 32-bit based XenServer dom0 sizeof(dma_addr_t) is 8.

Fix that by casting to unsigned long long a masking constant used by
the code. This resolves a crash in iser_sg_to_page_vec on this system.
Signed-off-by: NOr Gerlitz <ogerlitz@mellanox.co.il>
Signed-off-by: NRoland Dreier <roland@purestorage.com>