drm/bridge: lt9611: switch to of_drm_get_bridge_by_endpoint()

drm/bridge: lt9611: switch to of_drm_get_bridge_by_endpoint()

This driver calls drm_of_find_panel_or_bridge() with a NULL pointer in the
@panel parameter, thus using a reduced feature set of that function.
Replace this call with the simpler of_drm_get_bridge_by_endpoint().

Since of_drm_get_bridge_by_endpoint() increases the refcount of the
returned bridge, ensure it is put on removal. To achieve this, instead of
adding an explicit drm_bridge_put(), migrate to the bridge::next_bridge
pointer which is automatically put when the bridge is eventually freed.

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
Link: https://patch.msgid.link/20260511-drm-bridge-alloc-getput-panel_or_bridge-v6-7-f61c9e498b3f@bootlin.com
Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>