drm: bridge: ldb: add missing \n in dev_warn() string

dev_warn() and similar require a training \n.

Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
Reviewed-by: Robert Foss <rfoss@kernel.org>
Signed-off-by: Robert Foss <rfoss@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230405081058.2347130-1-luca.ceresoli@bootlin.com