i40e: use a local variable instead of calculating multiple times

The computed result of I40E_MAX_VSI_QP * I40E_VIRTCHNL_SUPPORTED_QTYPES
is used more than three times in function i40e_config_irq_link_list.
Simply declare a local variable to store it to improve readability.

Signed-off-by: Lihong Yang <lihong.yang@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>