net/mlx5: Use first online CPU instead of hard coded CPU

Hard coded CPU (0 in our case) might be offline. Hence, use the first
online CPU instead.

Fixes: f891b7cd ("net/mlx5: Enable single IRQ for PCI Function")
Signed-off-by: Shay Drory <shayd@nvidia.com>
Reviewed-by: Moshe Shemesh <moshe@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>

drivers/net/ethernet/mellanox/mlx5/core/pci_irq.c

@@ -398,7 +398,7 @@ irq_pool_request_vector(struct mlx5_irq_pool *pool, int vecidx,
 	cpumask_copy(irq->mask, affinity);
 	if (!irq_pool_is_sf_pool(pool) && !pool->xa_num_irqs.max &&
 	    cpumask_empty(irq->mask))
-		cpumask_set_cpu(0, irq->mask);
+		cpumask_set_cpu(cpumask_first(cpu_online_mask), irq->mask);
 	irq_set_affinity_hint(irq->irqn, irq->mask);
 unlock:
 	mutex_unlock(&pool->lock);