drm/i915: unbreak lastclose for failed driver init

We now refuse to load on gen6+ if kms is not enabled:

commit 26394d92
Author: Daniel Vetter <daniel.vetter@ffwll.ch>
Date:   Mon Mar 26 21:33:18 2012 +0200

    drm/i915: refuse to load on gen6+ without kms

Which results in the drm core calling our lastclose function to clean
up the mess, but that one is neatly broken for such failure cases
since kms has been introduced in

commit 79e53945
Author: Jesse Barnes <jbarnes@virtuousgeek.org>
Date:   Fri Nov 7 14:24:08 2008 -0800

    DRM: i915: add mode setting support
Reported-and-tested-by: NPaulo Zanoni <przanoni@gmail.com>
Signed-Off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_dma.c

@@ -1781,7 +1781,13 @@ void i915_driver_lastclose(struct drm_device * dev)
 {
 	drm_i915_private_t *dev_priv = dev->dev_private;
 
-	if (!dev_priv || drm_core_check_feature(dev, DRIVER_MODESET)) {
+	/* On gen6+ we refuse to init without kms enabled, but then the drm core
+	 * goes right around and calls lastclose. Check for this and don't clean
+	 * up anything. */
+	if (!dev_priv)
+		return;
+
+	if (drm_core_check_feature(dev, DRIVER_MODESET)) {
 		intel_fb_restore_mode(dev);
 		vga_switcheroo_process_delayed_switch();
 		return;