x86/pvh: Use correct size value in GDT descriptor

The limit field in a GDT descriptor is an inclusive bound, and therefore
one less than the size of the covered range.

Reviewed-by: Jason Andryuk <jason.andryuk@amd.com>
Tested-by: Jason Andryuk <jason.andryuk@amd.com>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Message-ID: <20241009160438.3884381-9-ardb+git@google.com>
Signed-off-by: Juergen Gross <jgross@suse.com>