drm/radeon/kms: don't use 0 bpc for adjusting hdmi clock

If the bpc is set from the connector is 0, we then use it later to adjust
in a special case the HDMI pixel clock, however if the bpc is 0, we end up
passing a 0 pixel clock into the code.

I'm not sure if this is the correct answer or if we should avoid the HDMI
clock adjustment for 0 values.

This fixes a divide by 0 on my Llano system with a HDMI monitor and hdmi
audio enabled.
Reviewed-by: Alex Deucher <alexdeucher@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/radeon/atombios_crtc.c

@@ -554,7 +554,7 @@ static u32 atombios_adjust_pll(struct drm_crtc *crtc,
 		if (encoder->crtc == crtc) {
 			radeon_encoder = to_radeon_encoder(encoder);
 			connector = radeon_get_connector_for_encoder(encoder);
-			if (connector)
+			if (connector && connector->display_info.bpc)
 				bpc = connector->display_info.bpc;
 			encoder_mode = atombios_get_encoder_mode(encoder);
 			if ((radeon_encoder->devices & (ATOM_DEVICE_LCD_SUPPORT | ATOM_DEVICE_DFP_SUPPORT)) ||