i40e: ShadowRAM checksum calculation change

Due to changes in FW the SW is required to perform double SR dump in
some cases.

Implementation adds two new steps to update nvm checksum function:
* recalculate checksum and check if checksum in NVM is correct
* if checksum in NVM is not correct then update it again

Signed-off-by: Maciej Paczkowski <maciej.paczkowski@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>