uas: Only complain about missing sg if all other checks succeed

commit cc4deafc upstream.

Don't complain about controllers without sg support if there are other
reasons why uas cannot be used anyways.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>