A stream may specify a rate range using 'rate_min' and 'rate_max', so a
stream may be valid and not specify any rates. However, as stream cannot
be valid and not have any channel. Let's use this condition instead to
determine if a stream is valid or not.

Fixes: cde79035 ("ASoC: Handle multiple codecs with split playback / capture")
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Signed-off-by: Mark Brown <broonie@kernel.org>