ixgbe: correct typo in define name

VF Free Running Timer register name missing an F.

Signed-off-by: Emil Tantilov <emil.s.tantilov@intel.com>
Acked-by: Greg Rose <gregory.v.rose@intel.com>
Tested-by: Evan Swanson <evan.swanson@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>