drivers: gpu: Mark function as static in r600_hdmi.c

Mark function r600_audio_set_dto() as static in drm/radeon/r600_hdmi.c
because it is not used outside this file.

This eliminates the following warning in drm/radeon/r600_hdmi.c:
drivers/gpu/drm/radeon/r600_hdmi.c:253:6: warning: no previous prototype for ‘r600_audio_set_dto’ [-Wmissing-prototypes]
Signed-off-by: NRashika Kheria <rashika.kheria@gmail.com>
Reviewed-by: NJosh Triplett <josh@joshtriplett.org>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/radeon/r600_hdmi.c

@@ -250,7 +250,7 @@ static void r600_hdmi_audio_workaround(struct drm_encoder *encoder)
 		 value, ~HDMI0_AUDIO_TEST_EN);
 }
 
-void r600_audio_set_dto(struct drm_encoder *encoder, u32 clock)
+static void r600_audio_set_dto(struct drm_encoder *encoder, u32 clock)
 {
 	struct drm_device *dev = encoder->dev;
 	struct radeon_device *rdev = dev->dev_private;