rcar-hpbdma: add parameter to set_slave() method

Commit 4981c4dc (DMA: shdma: switch DT mode to
use configuration data from a match table) added a new parameter to set_slave()
method but unfortunately got merged later than commit c4f6c41b
(dma: add driver for R-Car HPB-DMAC), so that the HPB-DMAC driver retained the
old prototype which caused this warning:

drivers/dma/sh/rcar-hpbdma.c:485: warning: initialization from incompatible
pointer type

The newly added parameter  is used to override DMA slave address from 'struct
hpb_dmae_slave_config', so we have to add the 'slave_addr' field to 'struct
hpb_dmae_chan', conditionally assign it in set_slave() method, and return in
slave_addr() method.

Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Tested-by: Simon Horman <horms+renesas@verge.net.au>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>