IB/uverbs: Initialize ib_qp_init_attr with zeros

Initialize ib_qp_init_attr with zeros in order to avoid from garbage
in fields that won't be set with user values.

Fixes: a060b562 ('IB/core: generic RDMA READ/WRITE API')
Signed-off-by: Maor Gottlieb <maorg@mellanox.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Doug Ledford <dledford@redhat.com>