e1000: fix sparse warning

Sparse complains because the e1000 driver is calling ioread on a pointer
not tagged as __iomem.

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Reviewed-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Tested-by: Jeff Pieper <jeffrey.e.pieper@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>