drm/exynos: dsi: Remove bridge node reference in removal

Since bridge node is referenced during in the probe, it should be
released on removal.

Suggested-by: Andrzej Hajda <a.hajda@samsung.com>
Signed-off-by: Hoegeun Kwon <hoegeun.kwon@samsung.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>