Return -ENODEV rather than -EINVAL on probe errors due to a missing
endpoint.

Also clean up the endpoint sanity check somewhat and use the interface
device for logging a more compact error in case an expected endpoint is
missing.
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Johan Hovold <johan@kernel.org>