drm/exynos: Don't reset bridge->next

bridge->next is only points to the new bridge if drm_bridge_attach()
succeeds. No need to reset it manually here.

Note that this change is part of the attempt to make the bridge chain
a double-linked list. In order to do that we must patch all drivers
manipulating the bridge->next field.

Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Inki Dae <inki.dae@samsung.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191023154512.9762-3-boris.brezillon@collabora.com