drm/tilcdc: Remove redundant OF_DETACHED flag setting

of_fdt_unflatten_tree() already sets the flag on this node to
OF_DETACHED, because of_fdt_unflatten_tree() calls
__unflatten_device_tree() with the detached bool set to true.

Cc: Rob Herring <robh+dt@kernel.org>
Cc: Frank Rowand <frowand.list@gmail.com>
Signed-off-by: Stephen Boyd <stephen.boyd@linaro.org>
Signed-off-by: Jyri Sarha <jsarha@ti.com>