ALSA: hda/hdmi: Replace zero-length array with DECLARE_FLEX_ARRAY() helper

Zero-length arrays are deprecated and we are moving towards adopting
C99 flexible-array members, instead. So, replace zero-length array
declaration in union audio_infoframe with the new DECLARE_FLEX_ARRAY()
helper macro.

This helper allows for a flexible-array member in a union.

Link: https://github.com/KSPP/linux/issues/193
Link: https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.htmlSigned-off-by: NGustavo A. R. Silva <gustavoars@kernel.org>
Reviewed-by: NKees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/Yw01A+TvF1FWQ588@workSigned-off-by: NTakashi Iwai <tiwai@suse.de>

sound/pci/hda/patch_hdmi.c

@@ -229,7 +229,7 @@ struct dp_audio_infoframe {
 union audio_infoframe {
 	struct hdmi_audio_infoframe hdmi;
 	struct dp_audio_infoframe dp;
-	u8 bytes[0];
+	DECLARE_FLEX_ARRAY(u8, bytes);
 };
 
 /*