mcb: Add a dma_device to mcb_device

mcb: Add a dma_device to mcb_device

When performing DMA operations on a MCB device, the device needed
for using the DMA API is "mcb_device->bus_carrier".
This is rather lengthy, so a shortcut is introduced to struct mcb_device
in order to ensure the MCB device driver uses the correct device for DMA
operations.

Signed-off-by: Michael Moese <michael.moese@men.de>
Signed-off-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>