drm/i915: Make intel_panel_get_backlight static.

This function isn't used outside of intel_panel.c, so make it static.

Signed-off-by: Stéphane Marchesin <marcheu@chromium.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/intel_panel.c b/drivers/gpu/drm/i915/intel_panel.c
index 10c7d39..9474488d 100644
--- a/drivers/gpu/drm/i915/intel_panel.c
+++ b/drivers/gpu/drm/i915/intel_panel.c
@@ -213,7 +213,7 @@
 	return val;
 }
 
-u32 intel_panel_get_backlight(struct drm_device *dev)
+static u32 intel_panel_get_backlight(struct drm_device *dev)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
 	u32 val;