net/mlx4_core: clean up cq_res_start_move_to()

Building resource_tracker.o triggers a GCC warning:
    drivers/net/ethernet/mellanox/mlx4/resource_tracker.c: In function 'mlx4_HW2SW_CQ_wrapper':
    drivers/net/ethernet/mellanox/mlx4/resource_tracker.c:3019:16: warning: 'cq' may be used uninitialized in this function [-Wmaybe-uninitialized]
      atomic_dec(&cq->mtt->ref_count);
                    ^

This is a false positive. But a cleanup of cq_res_start_move_to() can
help GCC here. The code currently uses a switch statement where an
if/else construct would do too, since only two of the switch's four
cases can ever occur. Dropping that switch makes the warning go away.

While we're at it, add some missing braces.

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Signed-off-by: David S. Miller <davem@davemloft.net>