m501fb: don't return zero on failure path in sm501fb_probe()

If no framebuffers found, sm501fb_probe() breaks off initialization,
deallocates sm501fb_info, but returns zero. As a result, use after free
can happen in sm501fb_remove().

The patch adds -ENODEV as a return value in this case.

Found by Linux Driver Verification project (linuxtesting.org).
Signed-off-by: NAlexey Khoroshilov <khoroshilov@ispras.ru>
Signed-off-by: NTomi Valkeinen <tomi.valkeinen@ti.com>

drivers/video/fbdev/sm501fb.c

@@ -1988,6 +1988,7 @@ static int sm501fb_probe(struct platform_device *pdev)
 	if (info->fb[HEAD_PANEL] == NULL &&
 	    info->fb[HEAD_CRT] == NULL) {
 		dev_err(dev, "no framebuffers found\n");
+		ret = -ENODEV;
 		goto err_alloc;
 	}