hw/misc/vmlaunchupdate: do not clear control bits upon fw-cfg select op

The control bits define the behavior of the interface and clearing the bits
upon reading or select operation will break that behavior. For example, after
CTL_HOST_IGVM is set by the guest through a write and then subsequently, if the
guest tried to read back the values from the fw-cfg interface, the read would
clear CTL_HOST_IGVM. This would break restoring the host IGVM upon subsequent
reset.

Fixes: 30688c02a76e50e4 ("hw/misc/vmlaunchupdate: Introduce hypervisor fw-cfg interface support")
Signed-off-by: Ani Sinha <anisinha@redhat.com>
Message-ID: <20260825124139.6900-1-anisinha@redhat.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>