i40e: remove client instance on driver unload

When the driver is unloaded, we need to remove the client instance,
otherwise we leak memory.

Change-ID: If1e7882ac1f6ce15d004722fafbe31afbe0adc9a
Signed-off-by: Mitch Williams <mitch.a.williams@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>