ASoC: Intel: Skylake: Correct the handling of fmt_config flexible array

The struct nhlt_format's fmt_config is a flexible array, it must not be
used as normal array.
When moving to the next nhlt_fmt_cfg we need to take into account the data
behind the ->config.caps (indicated by ->config.size).

The logic of the code also changed: it is no longer saves the _last_
fmt_cfg for all found rates.

Fixes: bc2bd45b

 ("ASoC: Intel: Skylake: Parse nhlt and register clock device")
Signed-off-by: Peter Ujfalusi <peter.ujfalusi@linux.intel.com>
Reviewed-by: Cezary Rojewski <cezary.rojewski@intel.com>
Link: https://lore.kernel.org/r/20220630065638.11183-3-peter.ujfalusi@linux.intel.com
Signed-off-by: Mark Brown <broonie@kernel.org>