RDMA/qedr: Zero stack memory before copying to user space

The fact this struct was not init'd like all the others was missed when
the padding reserved field was added.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Fixes: 71e80a47 ("RDMA/qedr: Fix uABI structure layouts for 32/64 compat")
Acked-by: Michal Kalderon <Michal.Kalderon@cavium.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>