i40e: remove unused argument

With the final edition of the patches to remove sleeps from
the driver's entry points, the grab_rtnl argument is no
longer needed, so partially revert the commit that added it.

Change-ID: Ib9778476242586cc9e58b670f5f48d415cb59003
Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>