i40e: Fix mismatching type for ioremap_len

As pointed out by Ben Hutchings, ioremap uses unsigned long as
its parameter type, so we should be using that instead of u32
or int.

Reported-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>