pckbd: clear outport_present in outer pre_load()

The variable outport_present is a flag to show if the outport
subsection was loaded. Clear the outport_present flag in the
outer pre_load() function. This method is recommended in the QEMU
manual for developers in the chapter "Migration, Subsections".

Signed-off-by: Volker Rümelin <vr_qemu@t-online.de>
Message-Id: <20210525181441.27768-12-vr_qemu@t-online.de>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>