i40e: add hw struct local variable

This function uses the i40e_hw struct all over the place, so why doesn't
it keep a pointer to the struct? Add this pointer as a local variable
and use it consistently throughout the function.

Change-ID: I10eb688fe40909433fcb8ac7ac891cef67445d72
Signed-off-by: Mitch Williams <mitch.a.williams@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>