RDMA/hns: fix potential integer overflow on left shift

There is a potential integer overflow when int i is left shifted as this
is evaluated using 32 bit arithmetic but is being used in a context that
expects an expression of type dma_addr_t.  Fix this by casting integer i
to dma_addr_t before shifting to avoid the overflow.

Addresses-Coverity: ("Unintentional integer overflow")
Fixes: 2ac0bc5e

 ("RDMA/hns: Add a group interfaces for optimizing buffers getting flow")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>