[media] omap3isp: queue: Don't corrupt buf->npages when get_user_pages() fails

get_user_pages() can return a negative error code when it fails. Set
buf->npages to 0 in that case, to prevent isp_video_buffer_cleanup()
from releasing invalid pages.
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/video/omap3isp/ispqueue.c

@@ -339,7 +339,7 @@ static int isp_video_buffer_prepare_user(struct isp_video_buffer *buf)
 	up_read(&current->mm->mmap_sem);
 
 	if (ret != buf->npages) {
-		buf->npages = ret;
+		buf->npages = ret < 0 ? 0 : ret;
 		isp_video_buffer_cleanup(buf);
 		return -EFAULT;
 	}