sched: fix return value of wait_for_completion_interruptible()

The recent wait_for_completion() cleanups:

    commit 8cbbe86d
    Author: Andi Kleen <ak@suse.de>
    Date:   Mon Oct 15 17:00:14 2007 +0200

    sched: cleanup: refactor common code of sleep_on / wait_for_completion

    Refactor common code of sleep_on / wait_for_completion

broke the return value of wait_for_completion_interruptible().
Previously it returned 0 on success, now -1.  Fix that.

Problem found by Geert Uytterhoeven.

[ mingo: fixed whitespace damage ]
Reported-by: NGeert Uytterhoeven <Geert.Uytterhoeven@sonycom.com>
Signed-off-by: NAndi Kleen <ak@suse.de>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

kernel/sched.c

@@ -3859,7 +3859,10 @@ EXPORT_SYMBOL(wait_for_completion_timeout);
 
 int __sched wait_for_completion_interruptible(struct completion *x)
 {
-	return wait_for_common(x, MAX_SCHEDULE_TIMEOUT, TASK_INTERRUPTIBLE);
+	long t = wait_for_common(x, MAX_SCHEDULE_TIMEOUT, TASK_INTERRUPTIBLE);
+	if (t == -ERESTARTSYS)
+		return t;
+	return 0;
 }
 EXPORT_SYMBOL(wait_for_completion_interruptible);