drm/mcde: Use drmm_add_final_kfree

With this we can drop the final kfree from the release function.

v2: Fix unused variable warning, spotted while applying.
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Linus Walleij <linus.walleij@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200323144950.3018436-13-daniel.vetter@ffwll.ch

drivers/gpu/drm/mcde/mcde_drv.c

@@ -72,6 +72,7 @@
 #include <drm/drm_gem.h>
 #include <drm/drm_gem_cma_helper.h>
 #include <drm/drm_gem_framebuffer_helper.h>
+#include <drm/drm_managed.h>
 #include <drm/drm_of.h>
 #include <drm/drm_probe_helper.h>
 #include <drm/drm_panel.h>
@@ -219,11 +220,8 @@ static int mcde_modeset_init(struct drm_device *drm)
 
 static void mcde_release(struct drm_device *drm)
 {
-	struct mcde *mcde = drm->dev_private;
-
 	drm_mode_config_cleanup(drm);
 	drm_dev_fini(drm);
-	kfree(mcde);
 }
 
 DEFINE_DRM_GEM_CMA_FOPS(drm_fops);
@@ -330,6 +328,7 @@ static int mcde_probe(struct platform_device *pdev)
 	}
 	drm = &mcde->drm;
 	drm->dev_private = mcde;
+	drmm_add_final_kfree(drm, mcde);
 	platform_set_drvdata(pdev, drm);
 
 	/* Enable continuous updates: this is what Linux' framebuffer expects */