airo: use simple_write_to_buffer

Simplify write file operation for /proc files by using
simple_write_to_buffer().

Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Cc: "John W. Linville" <linville@tuxdriver.com>
Cc: linux-wireless@vger.kernel.org
Cc: netdev@vger.kernel.org
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/airo.c

@@ -4652,24 +4652,18 @@ static ssize_t proc_write( struct file *file,
 			   size_t len,
 			   loff_t *offset )
 {
-	loff_t pos = *offset;
+	ssize_t ret;
 	struct proc_data *priv = file->private_data;
 
 	if (!priv->wbuffer)
 		return -EINVAL;
 
-	if (pos < 0)
-		return -EINVAL;
-	if (pos >= priv->maxwritelen)
-		return 0;
-	if (len > priv->maxwritelen - pos)
-		len = priv->maxwritelen - pos;
-	if (copy_from_user(priv->wbuffer + pos, buffer, len))
-		return -EFAULT;
-	if ( pos + len > priv->writelen )
-		priv->writelen = len + file->f_pos;
-	*offset = pos + len;
-	return len;
+	ret = simple_write_to_buffer(priv->wbuffer, priv->maxwritelen, offset,
+					buffer, len);
+	if (ret > 0)
+		priv->writelen = max_t(int, priv->writelen, *offset);
+
+	return ret;
 }
 
 static int proc_status_open(struct inode *inode, struct file *file)