i40e: Fix for division by zero

For some cases when reading from device are incorrect or image is
incorrect, this part of code causes crash due to division by zero.

Change-ID: I8961029a7a87b0a479995823ef8fcbf6471405e1
Signed-off-by: Michal Kosiarz <michal.kosiarz@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>