drm/i915: fix uninitialized variable warning in i915_setup_compression()

Fixes:

drivers/gpu/drm/i915/i915_dma.c: In function ‘i915_setup_compression’:
drivers/gpu/drm/i915/i915_dma.c:1311: error: ‘compressed_llb’ may be used uninitialized in this function
Signed-off-by: NPrarit Bhargava <prarit@redhat.com>
Signed-off-by: NEric Anholt <eric@anholt.net>

drivers/gpu/drm/i915/i915_dma.c

@@ -1231,7 +1231,7 @@ static void i915_warn_stolen(struct drm_device *dev)
 static void i915_setup_compression(struct drm_device *dev, int size)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
-	struct drm_mm_node *compressed_fb, *compressed_llb;
+	struct drm_mm_node *compressed_fb, *uninitialized_var(compressed_llb);
 	unsigned long cfb_base;
 	unsigned long ll_base = 0;