ASoC: Use __printf markup to silence compiler

Silence warnings (triggered at W=1) by adding relevant __printf
attributes.

  sound/soc/soc-dapm.c:149:2: warning: function 'pop_dbg' might be a candidate for 'gnu_printf' format attribute [-Wsuggest-attribute=format]
Signed-off-by: Mathieu Malaterre <malat@debian.org>
Signed-off-by: Mark Brown <broonie@kernel.org>

sound/soc/soc-dapm.c

@@ -157,6 +157,7 @@ static void pop_wait(u32 pop_time)
 		schedule_timeout_uninterruptible(msecs_to_jiffies(pop_time));
 }
 
+__printf(3, 4)
 static void pop_dbg(struct device *dev, u32 pop_time, const char *fmt, ...)
 {
 	va_list args;