Include linux/kaiser.h instead of asm/kaiser.h to build ldt.c without
CONFIG_KAISER.  kaiser_add_mapping() does already return an error code,
so fix the FIXME.
Acked-by: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

CVE-2017-5754
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>