RDMA/efa: Rename vector field in efa_irq struct to irqn

The vector field naming is quite confusing, it is better referred to as
irqn.

Link: https://lore.kernel.org/r/20210811151131.39138-4-galpress@amazon.com


Reviewed-by: Firas JahJah <firasj@amazon.com>
Reviewed-by: Yossi Leybovich <sleybo@amazon.com>
Signed-off-by: Gal Pressman <galpress@amazon.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>