i40e: fix shifts of signed values

This patch fixes following error reported by cppcheck:
(error) Shifting signed 32-bit value by 31 bits is undefined behaviour

Signed-off-by: Beilei Xing <beilei.xing@intel.com>
Signed-off-by: Ferruh Yigit <ferruh.yigit@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>