x86/ldt: fix crash in ldt freeing.

x86/ldt: fix crash in ldt freeing.

94b1f3e2c4b7 (kaiser: merged update) factored out __free_ldt_struct() to
use vfree/free_page, but in the page allocation case it is actually
allocated with kmalloc so needs to be freed with kfree and not
free_page().

Reported-by: Vegard Nossum <vegard.nossum@oracle.com>
Signed-off-by: Jamie Iles <jamie.iles@oracle.com>
Orabug: 27333760
CVE: CVE-2017-5754
Signed-off-by: Pavel Tatashin <pasha.tatashin@oracle.com>
Signed-off-by: Kirtikar Kashyap <kirtikar.kashyap@oracle.com>