ata: sata_dwc_460ex: supply physical address of FIFO to DMA

DMA operates with physical addresses which is not exactly the same as ioremap()
returns.

Introduce variable to keep physical address of the SATA FIFO register and
supply it when prepare DMA channel.

Tested-by: Christian Lamparter <chunkeey@googlemail.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Tejun Heo <tj@kernel.org>