mlx4: remove unused fields

This also can address following UBSAN warnings:
[   36.640343] ================================================================================
[   36.648772] UBSAN: Undefined behaviour in drivers/net/ethernet/mellanox/mlx4/fw.c:857:26
[   36.656853] shift exponent 64 is too large for 32-bit type 'int'
[   36.663348] ================================================================================
[   36.671783] ================================================================================
[   36.680213] UBSAN: Undefined behaviour in drivers/net/ethernet/mellanox/mlx4/fw.c:861:27
[   36.688297] shift exponent 35 is too large for 32-bit type 'int'
[   36.694702] ================================================================================

Tested:
  reboot with UBSAN, no warning.

Signed-off-by: David Decotigny <decot@googlers.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Tariq Toukan <tariqt@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>