ixgbe: Clean up type inconsistency

Missed this when I created commit 6a14ee0c ("ixgbe: Add X550 support
function pointers").  Use a the __be* type to be consistent with how the
value is assigned.

CC: <kernel-team@fb.com>
Signed-off-by: Don Skidmore <donald.c.skidmore@intel.com>
Tested-by: Phil Schmitt <phillip.j.schmitt@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>