mISDN: fix race in timer canceling on module unloading

Using timer_pending() without additional syncronization is racy,
del_timer_sync() must be used here for waiting in-flight handler.
Bug caught with help from "debug-objects" during random insmod/rmmod.

Signed-off-by: Konstantin Khlebnikov <khlebnikov@openvz.org>
Cc: Karsten Keil <isdn@linux-pingi.de>
Cc: David S. Miller <davem@davemloft.net>
Cc: netdev <netdev@vger.kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/isdn/mISDN/dsp_core.c

@@ -1217,8 +1217,7 @@ static void __exit dsp_cleanup(void)
 {
 	mISDN_unregister_Bprotocol(&DSP);
 
-	if (timer_pending(&dsp_spl_tl))
-		del_timer(&dsp_spl_tl);
+	del_timer_sync(&dsp_spl_tl);
 
 	if (!list_empty(&dsp_ilist)) {
 		printk(KERN_ERR "mISDN_dsp: Audio DSP object inst list not "