i40e: fix shift precedence issue

Add parens to make sure the shift and bitwise precedences don't work backwards
for us.

Change-ID: I60c10ef4fad6bc654522b9d8a53da2e270a0f268
Reported-by: Joe Perches <joe@perches.com>
Signed-off-by: Shannon Nelson <shannon.nelson@intel.com>
Tested-by: Jim Young <james.m.young@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>