hw/audio/gus: Fix registers 32-bit access

hw/audio/gus: Fix registers 32-bit access

Fix audio on software that accesses DRAM above 64k via register
peek/poke and some cases when more than 16 voices are used.

Cc: qemu-stable@nongnu.org
Fixes: 135f5ae1974c ("audio: GUSsample is int16_t")
Signed-off-by: Allan Peramaki <aperamak@pp1.inet.fi>
Tested-by: Volker Rümelin <vr_qemu@t-online.de>
Reviewed-by: Volker Rümelin <vr_qemu@t-online.de>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-id: 20200618103623.6031-1-philmd@redhat.com
Message-Id: <20200615201757.16868-1-aperamak@pp1.inet.fi>
[PMD: Removed unrelated style changes]
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>