i40e: Fix a message string

Change string from "Side Band" to "Sideband" for consistency.

Change-ID: I45f05466bb5c63b0f999d743312bcb61b5bd6518
Signed-off-by: Anjali Singhai Jain <anjali.singhai@intel.com>
Signed-off-by: Catherine Sullivan <catherine.sullivan@intel.com>
Tested-by: Kavindya Deegala <kavindya.s.deegala@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>