drm/i915: add some runtime PM get/put calls

These are needed when we cat the debugfs and sysfs files.

V2: - Rebase
V3: - Rebase
V4: - Rebase

Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@gmail.com>
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 b0f6e6c..20ebc3e 100644
--- a/drivers/gpu/drm/i915/intel_panel.c
+++ b/drivers/gpu/drm/i915/intel_panel.c
@@ -845,11 +845,14 @@
 {
 	struct intel_connector *connector = bl_get_data(bd);
 	struct drm_device *dev = connector->base.dev;
+	struct drm_i915_private *dev_priv = dev->dev_private;
 	int ret;
 
+	intel_runtime_pm_get(dev_priv);
 	mutex_lock(&dev->mode_config.mutex);
 	ret = intel_panel_get_backlight(connector);
 	mutex_unlock(&dev->mode_config.mutex);
+	intel_runtime_pm_put(dev_priv);
 
 	return ret;
 }