mlx4_core: map async events to arbitrary slave eqs

Slave async events were mapped to single eq. This patch fixes this issue, so
the slaves can map the async events to any eq.

Signed-off-by: Marcel Apfelbaum <marcela@dev.mellanox.co.il>
Reviewed-by: Jack Morgenstein <jackm@dev.mellanox.co.il>
Signed-off-by: David S. Miller <davem@davemloft.net>