ata: sata_dwc_460ex: set dma_boundary to 0x1fff

The original code states:

	Make sure a LLI block is not created that will span 8K max FIS
	boundary. If the block spans such a FIS boundary, there is a chance
	that a DMA burst will cross that boundary -- this results in an error
	in the host controller.

Since we have switched to generic DMAengine API we satisfy above by setting
dma_boundary value to 0x1fff.

Suggested-by: Mans Rullgard <mans@mansr.com>
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>