ASoC: component: suppress uninitialized-variable warning

Old versions of gcc (tested on gcc-4.8) produce a warning for
correct code:

sound/soc/soc-compress.c: In function 'soc_compr_open':
sound/soc/soc-compress.c:75:28: error: 'component' is used uninitialized in this function [-Werror=uninitialized]
  struct snd_soc_component *component, *save = NULL;

Change the for_each_rtd_components() macro to ensure 'component'
gets initialized to a value the compiler does not complain about.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20200428214754.3925368-1-arnd@arndb.deSigned-off-by: Mark Brown <broonie@kernel.org>

include/sound/soc.h

@@ -1179,7 +1179,7 @@ struct snd_soc_pcm_runtime {
 #define asoc_rtd_to_codec(rtd, n) (rtd)->dais[n + (rtd)->num_cpus]
 
 #define for_each_rtd_components(rtd, i, component)			\
-	for ((i) = 0;							\
+	for ((i) = 0, component = NULL;					\
 	     ((i) < rtd->num_components) && ((component) = rtd->components[i]);\
 	     (i)++)
 #define for_each_rtd_cpu_dais(rtd, i, dai)				\