drm/bridge: anx6345: Fix compilation breakage on systems without CONFIG_OF

The driver assumes that the platform uses the device tree, and thus relies
on some fields (of_node) being declared in some structures (drm_bridge).

This isn't true for all platforms, so make sure we can only compile the
ANX6345 on platforms where DT support is selected.

Cc: Torsten Duwe <duwe@lst.de>
Fixes: 6aa19269 ("drm/bridge: Add Analogix anx6345 support")
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://patchwork.freedesktop.org/patch/msgid/20191112204551.541449-1-maxime@cerno.tech

drivers/gpu/drm/bridge/analogix/Kconfig

 # SPDX-License-Identifier: GPL-2.0-only
 config DRM_ANALOGIX_ANX6345
 	tristate "Analogix ANX6345 bridge"
+	depends on OF
 	select DRM_ANALOGIX_DP
 	select DRM_KMS_HELPER
 	select REGMAP_I2C