i40e: fix kbuild warnings

The 0day build infrastructure found some issues in i40e, this
removes the warnings by adding a harmless cast to a dev_info.

CC: kbuild-all@01.org
Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Reported-by: kbuild test robot <fengguang.wu@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>