staging/olpc_docn: reorder the lock sequence to avoid potential dead lock

The lock sequence of dcon_blank_fb(fb_info->lock ---> console_lock) is against
with the one of console_callback(console_lock ---> fb_info->lock), it'll
lead to a potential dead lock, so reorder the lock sequence of dcon_blank_fb
to avoid the potential dead lock.
Signed-off-by: Gu Zheng <guz.fnst@cn.fujitsu.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/olpc_dcon/olpc_dcon.c

@@ -255,17 +255,19 @@ static bool dcon_blank_fb(struct dcon_priv *dcon, bool blank)
 {
 	int err;
 
+	console_lock();
 	if (!lock_fb_info(dcon->fbinfo)) {
+		console_unlock();
 		dev_err(&dcon->client->dev, "unable to lock framebuffer\n");
 		return false;
 	}
-	console_lock();
+
 	dcon->ignore_fb_events = true;
 	err = fb_blank(dcon->fbinfo,
 			blank ? FB_BLANK_POWERDOWN : FB_BLANK_UNBLANK);
 	dcon->ignore_fb_events = false;
-	console_unlock();
 	unlock_fb_info(dcon->fbinfo);
+	console_unlock();
 
 	if (err) {
 		dev_err(&dcon->client->dev, "couldn't %sblank framebuffer\n",