dsound: Get rid of no longer needed mix_buffer_len field.

This was missing in 09890d7142a2c612b025ab9ff60358d036f9999b.

Signed-off-by: Sebastian Lackner <sebastian@fds-team.de>
Signed-off-by: Andrew Eikum <aeikum@codeweavers.com>
Signed-off-by: Alexandre Julliard <julliard@winehq.org>
2 files changed