x86, vmi: fix broken LDT access

This one took a long time to rear up because LDT usage is not very
common, but the bug is quite serious.  It got introduced along with
another bug, already fixed, by 75b8bb3e



After investigating a JRE failure, I found this bug was introduced a long time
ago, and had already managed to survive another bugfix which occurred on the
same line.  The result is a total failure of the JRE due to LDT selectors not
working properly.

Signed-off-by: Zachary Amsden <zach@vmware.com>
Cc: Glauber de Oliveira Costa <gcosta@redhat.com>
Cc: stable@kernel.org
Signed-off-by: Ingo Molnar <mingo@elte.hu>