alpha: fix osf_wait4() breakage

kernel_wait4() expects a userland address for status - it's only
rusage that goes as a kernel one (and needs a copyout afterwards)

[ Also, fix the prototype of kernel_wait4() to have that __user
  annotation   - Linus ]

Fixes: 92ebce5ac55d ("osf_wait4: switch to kernel_wait4()")
Cc: stable@kernel.org # v4.13+
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/alpha/kernel/osf_sys.c

@@ -1180,13 +1180,10 @@ SYSCALL_DEFINE2(osf_getrusage, int, who, struct rusage32 __user *, ru)
 SYSCALL_DEFINE4(osf_wait4, pid_t, pid, int __user *, ustatus, int, options,
 		struct rusage32 __user *, ur)
 {
-	unsigned int status = 0;
 	struct rusage r;
-	long err = kernel_wait4(pid, &status, options, &r);
+	long err = kernel_wait4(pid, ustatus, options, &r);
 	if (err <= 0)
 		return err;
-	if (put_user(status, ustatus))
-		return -EFAULT;
 	if (!ur)
 		return err;
 	if (put_tv_to_tv32(&ur->ru_utime, &r.ru_utime))

include/linux/sched/task.h

@@ -75,7 +75,7 @@ extern long _do_fork(unsigned long, unsigned long, unsigned long, int __user *,
 extern long do_fork(unsigned long, unsigned long, unsigned long, int __user *, int __user *);
 struct task_struct *fork_idle(int);
 extern pid_t kernel_thread(int (*fn)(void *), void *arg, unsigned long flags);
-extern long kernel_wait4(pid_t, int *, int, struct rusage *);
+extern long kernel_wait4(pid_t, int __user *, int, struct rusage *);
 
 extern void free_task(struct task_struct *tsk);