i40e: Tx/Rx rings declaration

This patch changes the declaration of Tx/Rx rings inside several loops. It
eliminates declaring the same rings every time for the duration of the loop,
instead declaring them once before the loop.

Change-ID: I59dea54276f18c47dca522f520c18f65fe42a15d
Signed-off-by: Akeem G Abodunrin <akeem.g.abodunrin@intel.com>
Tested-by: Kavindya Deegala <kavindya.s.deegala@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>