drm/bridge: dw-hdmi: Staticize dw_hdmi_bridge_funcs

Staticize dw_hdmi_bridge_funcs to fix the following sparse warning:

drivers/gpu/drm/bridge/dw_hdmi.c:1458:25: warning: symbol 'dw_hdmi_bridge_funcs' was not declared. Should it be static?

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>