i40e: not compute affinity_mask for IRQ

After commit 759dc4a7 ("i40e: initialize our affinity_mask
based on cpu_possible_mask"), NAPI IRQ affinity_mask is bind to
all possible CPUs, not a fixed CPU

Signed-off-by: Li RongQing <lirongqing@baidu.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>