ixgbe: clean up ixgbe_atr_compute_perfect_hash_82599

Rather than assign several parameters in a row, we should use a for
loop, which reduces code size.

CC: Arun Sharma <asharma@fb.com>
Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Tested-by: Phil Schmitt <phillip.j.schmitt@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>