serial: sh-sci: don't filter on DMA device, use only channel ID

On some sh-mobile systems there are more than one DMA controllers, that
can be used for serial ports. Specifying a DMA device in sh-sci platform
data unnecessarily restricts the driver to only use one DMA controller.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
[Fixed the trivial conflict in include/linux/serial_sci.h]
Signed-off-by: Vinod Koul <vinod.koul@intel.com>