misc: genwqe: should return proper error value.

The function should return -EFAULT when copy_from_user fails. Even
though the caller does not distinguish them. but we should keep backward
compatibility.

Signed-off-by: zhong jiang <zhongjiang@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>