ASoC: SOF: Clean up sof_ipc_flood_dfs_write()

This function doesn't support partial writes so using
simple_write_to_buffer() doesn't really make sense.  It's better to
just use copy_from_user().
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Acked-by: Peter Ujfalusi <peter.ujfalusi@linux.intel.com>
Link: https://msgid.link/r/a35dded2-392b-4ccb-9dbb-d782ac9b6547@moroto.mountainSigned-off-by: Mark Brown <broonie@kernel.org>

sound/soc/sof/sof-client-ipc-flood-test.c

@@ -160,15 +160,20 @@ static ssize_t sof_ipc_flood_dfs_write(struct file *file, const char __user *buf
 	unsigned long ipc_count = 0;
 	struct dentry *dentry;
 	int err;
-	size_t size;
 	char *string;
 	int ret;
 
+	if (*ppos != 0)
+		return -EINVAL;
+
 	string = kzalloc(count + 1, GFP_KERNEL);
 	if (!string)
 		return -ENOMEM;
 
-	size = simple_write_to_buffer(string, count, ppos, buffer, count);
+	if (copy_from_user(string, buffer, count)) {
+		ret = -EFAULT;
+		goto out;
+	}
 
 	/*
 	 * write op is only supported for ipc_flood_count or
@@ -198,7 +203,7 @@ static ssize_t sof_ipc_flood_dfs_write(struct file *file, const char __user *buf
 	/* limit max duration/ipc count for flood test */
 	if (flood_duration_test) {
 		if (!ipc_duration_ms) {
-			ret = size;
+			ret = count;
 			goto out;
 		}
 
@@ -207,7 +212,7 @@ static ssize_t sof_ipc_flood_dfs_write(struct file *file, const char __user *buf
 			ipc_duration_ms = MAX_IPC_FLOOD_DURATION_MS;
 	} else {
 		if (!ipc_count) {
-			ret = size;
+			ret = count;
 			goto out;
 		}
 
@@ -231,9 +236,9 @@ static ssize_t sof_ipc_flood_dfs_write(struct file *file, const char __user *buf
 	if (err < 0)
 		dev_err_ratelimited(dev, "debugfs write failed to idle %d\n", err);
 
-	/* return size if test is successful */
+	/* return count if test is successful */
 	if (ret >= 0)
-		ret = size;
+		ret = count;
 out:
 	kfree(string);
 	return ret;