ASoC: stm: stm32_adfsdm: fix snprintf format string

ASoC: stm: stm32_adfsdm: fix snprintf format string

cppcheck warning:

sound/soc/stm/stm32_adfsdm.c:120:2: warning: %d in format
string (no. 1) requires 'int' but the argument type is 'unsigned
int'. [invalidPrintfArgType_sint]
 snprintf(str_freq, sizeof(str_freq), "%d\n", freq);
 ^

Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20210326215927.936377-11-pierre-louis.bossart@linux.intel.com
Signed-off-by: Mark Brown <broonie@kernel.org>