drm: bridge: dw-hdmi: fix building without CONFIG_OF

drm: bridge: dw-hdmi: fix building without CONFIG_OF

The of_node member in struct drm_bridge is hidden when CONFIG_OF
is disabled, causing a build error:

drivers/gpu/drm/bridge/dw-hdmi.c: In function '__dw_hdmi_probe':
drivers/gpu/drm/bridge/dw-hdmi.c:2063:14: error: 'struct drm_bridge' has no member named 'of_node'

We could fix this either using a Kconfig dependency on CONFIG_OF
or making the one line conditional. The latter gives us better
compile test coverage, so this is what I'm doing here.

Fixes: 69497eb9234e ("drm: bridge: dw-hdmi: Implement DRM bridge registration")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Archit Taneja <architt@codeaurora.org>
Link: http://patchwork.freedesktop.org/patch/msgid/20170123122312.3290934-1-arnd@arndb.de