ASoC: pcm: Fix (again) possible buffer overflow in dpcm state sysfs output

This is re-applying the fix that went into 5.6 (commit 6c89ffea)
as the changes were wiped out after merging the other code
refactoring.  Basically the same changes, just replacing the
suspicious calls of snprintf() with scnprintf().
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Link: https://lore.kernel.org/r/20200310163625.10838-1-tiwai@suse.deSigned-off-by: Mark Brown <broonie@kernel.org>

sound/soc/soc-pcm.c

@@ -66,16 +66,16 @@ static ssize_t dpcm_show_state(struct snd_soc_pcm_runtime *fe,
 	unsigned long flags;
 
 	/* FE state */
-	offset += snprintf(buf + offset, size - offset,
+	offset += scnprintf(buf + offset, size - offset,
 			   "[%s - %s]\n", fe->dai_link->name,
 			   stream ? "Capture" : "Playback");
 
-	offset += snprintf(buf + offset, size - offset, "State: %s\n",
+	offset += scnprintf(buf + offset, size - offset, "State: %s\n",
 			   dpcm_state_string(fe->dpcm[stream].state));
 
 	if ((fe->dpcm[stream].state >= SND_SOC_DPCM_STATE_HW_PARAMS) &&
 	    (fe->dpcm[stream].state <= SND_SOC_DPCM_STATE_STOP))
-		offset += snprintf(buf + offset, size - offset,
+		offset += scnprintf(buf + offset, size - offset,
 				   "Hardware Params: "
 				   "Format = %s, Channels = %d, Rate = %d\n",
 				   snd_pcm_format_name(params_format(params)),
@@ -83,10 +83,10 @@ static ssize_t dpcm_show_state(struct snd_soc_pcm_runtime *fe,
 				   params_rate(params));
 
 	/* BEs state */
-	offset += snprintf(buf + offset, size - offset, "Backends:\n");
+	offset += scnprintf(buf + offset, size - offset, "Backends:\n");
 
 	if (list_empty(&fe->dpcm[stream].be_clients)) {
-		offset += snprintf(buf + offset, size - offset,
+		offset += scnprintf(buf + offset, size - offset,
 				   " No active DSP links\n");
 		goto out;
 	}
@@ -96,16 +96,16 @@ static ssize_t dpcm_show_state(struct snd_soc_pcm_runtime *fe,
 		struct snd_soc_pcm_runtime *be = dpcm->be;
 		params = &dpcm->hw_params;
 
-		offset += snprintf(buf + offset, size - offset,
+		offset += scnprintf(buf + offset, size - offset,
 				   "- %s\n", be->dai_link->name);
 
-		offset += snprintf(buf + offset, size - offset,
+		offset += scnprintf(buf + offset, size - offset,
 				   "   State: %s\n",
 				   dpcm_state_string(be->dpcm[stream].state));
 
 		if ((be->dpcm[stream].state >= SND_SOC_DPCM_STATE_HW_PARAMS) &&
 		    (be->dpcm[stream].state <= SND_SOC_DPCM_STATE_STOP))
-			offset += snprintf(buf + offset, size - offset,
+			offset += scnprintf(buf + offset, size - offset,
 					   "   Hardware Params: "
 					   "Format = %s, Channels = %d, Rate = %d\n",
 					   snd_pcm_format_name(params_format(params)),