net/mlx4_core: Use correct variable type for mlx4_slave_cap

We've used an incorrect type for the loop counter and the
mlx4_QUERY_FUNC_CAP function. The current input modifier
is either a port or a boolean.
Since the number of ports is always a positive value < 255,
we should use u8 instead of an integer with casting.

Signed-off-by: Matan Barak <matanb@mellanox.com>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>