ASoC: intel: skl: Fix possible buffer overflow in debug outputs

The debugfs output of intel skl driver writes strings with multiple
snprintf() calls with the fixed size.  This was supposed to avoid the
buffer overflow but actually it still would, because snprintf()
returns the expected size to be output, not the actual output size.

Fix it by replacing snprintf() calls with scnprintf().

Fixes: d14700a0

 ("ASoC: Intel: Skylake: Debugfs facility to dump module config")
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Acked-by: Cezary Rojewski <cezary.rojewski@intel.com>
Link: https://lore.kernel.org/r/20200218111737.14193-3-tiwai@suse.de
Signed-off-by: Mark Brown <broonie@kernel.org>