i40evf: clean up local variable initialization

In i40evf_msix_aq(), the first two lines of rd32() are mainly to clear
the registers. If we initialize 'val' at this point, it will be
overwritten immediately. We shall simply discard the return value here.

When we initialize 'val', we might as well include the mask in one step.

Signed-off-by: Jean Sacren <sakiwit@gmail.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>