ASoC: hdmi-codec: remove unused spk_mask member

fix cppcheck warning:

sound/soc/codecs/hdmi-codec.c:25:16: style: struct member
'hdmi_codec_channel_map_table::spk_mask' is never
used. [unusedStructMember]
 unsigned long spk_mask;  /* speaker position bit mask */
               ^

Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20210312182246.5153-12-pierre-louis.bossart@linux.intel.com
Signed-off-by: Mark Brown <broonie@kernel.org>

sound/soc/codecs/hdmi-codec.c

@@ -22,7 +22,6 @@
 
 struct hdmi_codec_channel_map_table {
 	unsigned char map;	/* ALSA API channel map position */
-	unsigned long spk_mask;		/* speaker position bit mask */
 };
 
 /*