Simplify `foo == NULL || IS_ERR(foo)` via IS_ERR_OR_NULL(). This is
pretty commonly used all over the kernel, especially for debugfs/sysfs
cleanup paths.
Signed-off-by: NDavid Herrmann <dh.herrmann@gmail.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>