net/mlx4: Avoid 'may be used uninitialized' warnings

With a cross-compiler based on gcc-4.9, I see warnings like the following:

  drivers/net/ethernet/mellanox/mlx4/resource_tracker.c: In function 'mlx4_SW2HW_CQ_wrapper':
  drivers/net/ethernet/mellanox/mlx4/resource_tracker.c:3048:10: error: 'cq' may be used uninitialized in this function [-Werror=maybe-uninitialized]
    cq->mtt = mtt;

I think the warning is spurious because we only use cq when
cq_res_start_move_to() returns zero, and it always initializes *cq in that
case.  The srq case is similar.  But maybe gcc isn't smart enough to figure
that out.

Initialize cq and srq explicitly to avoid the warnings.

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>