drm/stm: Fix an error handling path in stm_drm_platform_probe()

If drm_dev_register() fails, a call to drv_load() must be undone, as
already done in the remove function.

Fixes: b759012c ("drm/stm: Add STM32 LTDC driver")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Acked-by: Raphael Gallais-Pou <raphael.gallais-pou@foss.st.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20fff7f853f20a48a96db8ff186124470ec4d976.1704560028.git.christophe.jaillet@wanadoo.frSigned-off-by: Raphael Gallais-Pou <raphael.gallais-pou@foss.st.com>

drivers/gpu/drm/stm/drv.c

@@ -203,12 +203,14 @@ static int stm_drm_platform_probe(struct platform_device *pdev)
 
 	ret = drm_dev_register(ddev, 0);
 	if (ret)
-		goto err_put;
+		goto err_unload;
 
 	drm_fbdev_dma_setup(ddev, 16);
 
 	return 0;
 
+err_unload:
+	drv_unload(ddev);
 err_put:
 	drm_dev_put(ddev);