staging: most: dim2-hdm: initialize DBR memory of synchronous channels

In the time after a synchronous DIM2 channel is enabled and before the
first buffer travels this channel, the DIM2 macro is babbling random
random data to the network.

This patch initializes the internal DBR memory of the DIM2 that is used
to transfer the synchronous data.

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>