drm/i915: Check for fused or unused pipes

We may have fused or unused pipes in our system. Let's check that the pipe
in question is within limits of accessible pipes. In case, that we are not
able to access the pipe, we return early with a warning.

v2: Rephrasing of the commit message (Jani)

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=103206Reported-by: NThomas Gleixner <tglx@linutronix.de>
Tested-by: NJaswinder Singh Rajput <jaswinder@perfectintelligent.com>
Suggested-by: NJani Nikula <jani.nikula@intel.com>
Reviewed-by: NJani Nikula <jani.nikula@intel.com>
Signed-off-by: NMika Kahola <mika.kahola@intel.com>
Signed-off-by: NJani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1513584243-12607-1-git-send-email-mika.kahola@intel.com

drivers/gpu/drm/i915/intel_audio.c

@@ -779,7 +779,7 @@ static struct intel_encoder *get_saved_enc(struct drm_i915_private *dev_priv,
 {
 	struct intel_encoder *encoder;
 
-	if (WARN_ON(pipe >= INTEL_INFO(dev_priv)->num_pipes))
+	if (WARN_ON(pipe >= ARRAY_SIZE(dev_priv->av_enc_map)))
 		return NULL;
 
 	/* MST */