RDMA/rxe: Fix error type of mmap_offset

RDMA/rxe: Fix error type of mmap_offset

[ Upstream commit 6ca18d8927d468c763571f78c9a7387a69ffa020 ]

The type of mmap_offset should be u64 instead of int to match the type of
mminfo.offset. If otherwise, after we create several thousands of CQs, it
will run into overflow issues.

Link: https://lore.kernel.org/r/20191227113613.5020-1-kejiewei.cn@gmail.com
Signed-off-by: Jiewei Ke <kejiewei.cn@gmail.com>
Reviewed-by: Jason Gunthorpe <jgg@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>