acpi/ghes: Change ghes fill logic to work with only one source

acpi/ghes: Change ghes fill logic to work with only one source

Extending to multiple sources require a BIOS pointer to the
beginning of the HEST table, which in turn requires a backward-compatible
code.

So, the current code supports only one source. Ensure that and simplify
the code.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Igor Mammedov <imammedo@redhat.com>
Message-Id: <66bddd42a64c8515ad98b9975d953b4a70ffcc6d.1736945236.git.mchehab+huawei@kernel.org>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>