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>