RDMA/nes: Fix incorrect casts on 32-bit architectures

The were some incorrect casts to unsigned long that caused 64-bit values
to be truncated on 32-bit architectures and made the driver pass invalid
adresses and lengths to the hardware.  The problems were primarily seen
with kernels with highmem configured but some could show up in
non-highmem kernels, too.

Signed-off-by: Don Wood <donald.e.wood@intel.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>