drm/radeon/kms: fix macbookpro connector quirk

Signed-off-by: NAlex Deucher <alexdeucher@gmail.com>
Signed-off-by: NDave Airlie <airlied@redhat.com>

drivers/gpu/drm/radeon/radeon_atombios.c

@@ -264,6 +264,8 @@ static bool radeon_atom_apply_quirks(struct drm_device *dev,
 		if ((supported_device == ATOM_DEVICE_CRT1_SUPPORT) ||
 		    (supported_device == ATOM_DEVICE_DFP2_SUPPORT))
 			return false;
+		if (supported_device == ATOM_DEVICE_CRT2_SUPPORT)
+			*line_mux = 0x90;
 	}
 
 	/* ASUS HD 3600 XT board lists the DVI port as HDMI */