net/mlx5: IRQ, consolidate irq and affinity mask allocation

Consolidate the mlx5_irq and mlx5_irq->mask allocation, to simplify
error flows and to match the dealloctation sequence @irq_release for
symmetry.

Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>
Reviewed-by: Shay Drory <shayd@nvidia.com>