i40e: use the more traditional 'i' loop variable

Since we no longer use i as an array index for the data variable,
replace the use of 'j' with 'i' so that we match the general loop
variable name.

Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>