compat: return -EFAULT on error in waitid()

The copy_to_user() call returns the number of bytes remaining but we
want to return -EFAULT on error.

Fixes "x32: fix waitid()"
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/compat.c

@@ -593,7 +593,7 @@ COMPAT_SYSCALL_DEFINE5(waitid,
 		else
 			ret = put_compat_rusage(&ru, uru);
 		if (ret)
-			return ret;
+			return -EFAULT;
 	}
 
 	BUG_ON(info.si_code & __SI_MASK);