drm/i915: Check num_pipes before initializing audio component

when num_pipes is zero, it indicates there is no display and HDMI
audio doesn't exist.

v2: Move the check from caller to callee for consistency.

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Signed-off-by: Elaine Wang <elaine.wang@intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1482142746-21663-1-git-send-email-elaine.wang@intel.com

drivers/gpu/drm/i915/intel_audio.c

@@ -928,6 +928,9 @@ void i915_audio_component_init(struct drm_i915_private *dev_priv)
 {
 	int ret;
 
+	if (INTEL_INFO(dev_priv)->num_pipes == 0)
+		return;
+
 	ret = component_add(dev_priv->drm.dev, &i915_audio_component_bind_ops);
 	if (ret < 0) {
 		DRM_ERROR("failed to add audio component (%d)\n", ret);