drm/i915/audio: fix hdmi audio noise issue

Some monitors will have noise or even no sound after
applying the patch 6014ac1.

In patch 6014ac1, it will reset the cts value to 0 for HDMI.
However, we need to disable Enable CTS or M Prog bit. This is
the initial setting after HW reset.

Fixes: 6014ac1 ("drm/i915/audio: set proper N/M in modeset")
Signed-off-by: Libin Yang <libin.yang@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1478853988-139842-1-git-send-email-libin.yang@intel.com

drivers/gpu/drm/i915/intel_audio.c

@@ -351,10 +351,13 @@ hsw_hdmi_audio_config_update(struct intel_crtc *intel_crtc, enum port port,
 
 	I915_WRITE(HSW_AUD_CFG(pipe), tmp);
 
+	/*
+	 * Let's disable "Enable CTS or M Prog bit"
+	 * and let HW calculate the value
+	 */
 	tmp = I915_READ(HSW_AUD_M_CTS_ENABLE(pipe));
-	tmp &= ~AUD_CONFIG_M_MASK;
+	tmp &= ~AUD_M_CTS_M_PROG_ENABLE;
 	tmp &= ~AUD_M_CTS_M_VALUE_INDEX;
-	tmp |= AUD_M_CTS_M_PROG_ENABLE;
 	I915_WRITE(HSW_AUD_M_CTS_ENABLE(pipe), tmp);
 }