configfs: use capped length for ->store_attribute()

The difference between "count" and "len" is that "len" is capped at
4095.  Changing it like this makes it match how sysfs_write_file() is
implemented.

This is a static analysis patch.  I haven't found any store_attribute()
functions where this change makes a difference.
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Joel Becker <jlbec@evilplan.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/configfs/file.c

@@ -203,7 +203,7 @@ configfs_write_file(struct file *file, const char __user *buf, size_t count, lof
 	mutex_lock(&buffer->mutex);
 	len = fill_write_buffer(buffer, buf, count);
 	if (len > 0)
-		len = flush_write_buffer(file->f_path.dentry, buffer, count);
+		len = flush_write_buffer(file->f_path.dentry, buffer, len);
 	if (len > 0)
 		*ppos += len;
 	mutex_unlock(&buffer->mutex);