i40e: Save PCI state before suspend

The i40e_suspend() function was failing to save PCI state
and this would result in a kernel stack trace from a WARN_ONCE in the
pci_legacy_suspend() function.

Add a call to pci_save_state() to fix that problem.

Change-ID: I4736e62bb660966bd208cc8af617a14cb07fc4bd
Signed-off-by: Greg Rose <gregory.v.rose@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>