i40evf: fix scan warning on sprintf

The driver was converted to use snprintf everywhere but this one function.
Just use snprintf, instead of sprintf.

Also a small spelling correction in a comment.

Change-ID: I59d45f94a52754c7b4cd6034df9a61d8132b7f77
Signed-off-by: Jesse Brandeburg <jesse.brandeburg@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>