hw/audio/fmopl: fix segmentation fault

hw/audio/fmopl: fix segmentation fault

Current code allocates the memory for ENV_CURVE too late. Move
allocation to OPLOpenTable() and deallocation to OPLCloseTable().

To reproduce the bug start qemu with -soundhw adlib.

Fixes 2eea51bd01 "hw/audio/fmopl: Move ENV_CURVE to .heap to save
32KiB of .bss"

Signed-off-by: Volker Rümelin <vr_qemu@t-online.de>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-id: 20200324061855.5951-1-vr_qemu@t-online.de
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>