s390/tape: Use del_timer_sync()

del_timer() does not wait for a possible running callback to
complete. So the call side might free request and the associated
objects while on another cpu the timer handler runs.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

drivers/s390/char/tape_std.c

@@ -78,7 +78,7 @@ tape_std_assign(struct tape_device *device)
 
 	rc = tape_do_io_interruptible(device, request);
 
-	del_timer(&timeout);
+	del_timer_sync(&timeout);
 
 	if (rc != 0) {
 		DBF_EVENT(3, "%08x: assign failed - device might be busy\n",