drm/debugfs: Drop conditionals around of_node pointers

Having conditional around the of_node pointer of the drm_bridge structure
is not necessary anymore, since drm_bridge structure always has the of_node
member since the commit d8dfccde ("drm/bridge: Drop conditionals around
of_node pointers").

So drop the conditional, please also note that this patch is following the
convention used by driver core, see commit c9e358df ("driver-core:
remove conditionals around devicetree pointers").

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Signed-off-by: Sui Jingfeng <sui.jingfeng@linux.dev>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240501051323.805076-1-sui.jingfeng@linux.dev