i40e: Replace strncpy with strlcpy to ensure null termination

Using strncpy allows destination buffer to be not null terminated
after the copying takes place. strlcpy ensures that's not the
case by explicitly setting last element in the buffer as '\0'.

Signed-off-by: Patryk Małek <patryk.malek@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>