net/mlx4: Fix fall-through warning for Clang

In preparation to enable -Wimplicit-fallthrough for Clang, fix a warning
by explicitly adding a break statement instead of just letting the code
fall through to the next case.

Link: https://github.com/KSPP/linux/issues/115
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>

drivers/net/ethernet/mellanox/mlx4/resource_tracker.c

@@ -2660,6 +2660,7 @@ int mlx4_FREE_RES_wrapper(struct mlx4_dev *dev, int slave,
 	case RES_XRCD:
 		err = xrcdn_free_res(dev, slave, vhcr->op_modifier, alop,
 				     vhcr->in_param, &vhcr->out_param);
+		break;
 
 	default:
 		break;