net/mlx5: Set all field of mlx5_irq before inserting it to the xarray

Currently irq->pool is set after the irq is insert to the xarray.
Set irq->pool before the irq is inserted to the xarray.

Fixes: 71e084e2 ("net/mlx5: Allocating a pool of MSI-X vectors for SFs")
Signed-off-by: Shay Drory <shayd@nvidia.com>
Reviewed-by: Parav Pandit <parav@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>