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: Alexey Khoroshilov <[e-mail]>
Signed-off-by: Tomi Valkeinen <[e-mail]>

drivers/video/fbdev/sm501fb.c

···
 	if (info->fb[HEAD_PANEL] == NULL &&
 	    info->fb[HEAD_CRT] == NULL) {
 		dev_err(dev, "no framebuffers found\n");
+		ret = -ENODEV;
 		goto err_alloc;
 	}