IB/mlx4: Don't use GFP_ATOMIC for CQ resize struct

We allocate a small tracking structure as part of mlx4_ib_resize_cq().
However, we don't need to use GFP_ATOMIC -- immediately after the
allocation, we call mlx4_cq_resize(), which allocates a command
mailbox with GFP_KERNEL and then sleeps on a firmware command, so we
better not be in an atomic context.

This actually has a real impact, because when this GFP_ATOMIC
allocation fails (and GFP_ATOMIC does fail in practice) then a
userspace consumer resizing a CQ will get a spurious failure that we
can easily avoid.

Signed-off-by: Roland Dreier <roland@purestorage.com>
Reviewed-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>