drm/msm: Fix possible uninitialized access in fbdev

Do not run drm_fb_helper_unprepare() if fbdev allocation fails. Avoids
access to an uninitialized pointer. Original bug report is at [1].
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Fixes: 3fb1f62f ("drm/fb-helper: Remove drm_fb_helper_unprepare() from drm_fb_helper_fini()")
Link: https://lore.kernel.org/oe-kbuild-all/202302220810.9dymwCQ8-lkp@intel.com/ # 1
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/523715/
Link: https://lore.kernel.org/r/20230222123712.5049-1-tzimmermann@suse.deSigned-off-by: Rob Clark <robdclark@chromium.org>

drivers/gpu/drm/msm/msm_fbdev.c

@@ -136,13 +136,13 @@ static const struct drm_fb_helper_funcs msm_fb_helper_funcs = {
 struct drm_fb_helper *msm_fbdev_init(struct drm_device *dev)
 {
 	struct msm_drm_private *priv = dev->dev_private;
-	struct msm_fbdev *fbdev = NULL;
+	struct msm_fbdev *fbdev;
 	struct drm_fb_helper *helper;
 	int ret;
 
 	fbdev = kzalloc(sizeof(*fbdev), GFP_KERNEL);
 	if (!fbdev)
-		goto fail;
+		return NULL;
 
 	helper = &fbdev->base;