spi: dw: Propagate struct device pointer to ->dma_init() callback

In some cases, one of which is coming soon, we would like to have
a struct device pointer to request DMA channel. For this purpose
propagate it to ->dma_init() callback in DMA ops.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20200506153025.21441-7-andriy.shevchenko@linux.intel.com
Signed-off-by: Mark Brown <broonie@kernel.org>