staging: most: hdm-dim2: round up DBR memory for async/ctrl

As the DBR memory is allocated in units of DBR_BLOCK_SIZE, it is more
efficient to configure the DIM2 IP to use whole blocks of the DBR memory.
This patch ceils the DBR memory size used by the DIM2 IP for async/ctrl
channels.

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>