staging: most: hdm-dim2: double size of DBR buffer

This patch increases the size of the asynchronous and control DBR buffers
in the Tx path to twice the max. message size. This patch is needed to
increase the throughput for big messages.

Signed-off-by: Andrey Shvetsov <andrey.shvetsov@k2l.de>
Signed-off-by: Christian Gromm <christian.gromm@microchip.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>