i40e: use correct vf_id offset for virtchnl message

The vf_id needs to be offset by the vf_base_id from hw function capabilities
for the case of multiple PFs.

Change-ID: I20ca8621f98e9cdf98649380b8eeaa35db52677c
Signed-off-by: Ashish Shah <ashish.n.shah@intel.com>
Tested-by: Sibai Li <sibai.li@intel.com>
Signed-off-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>