spi: dw: Zero DMA Tx and Rx configurations on stack

Some DMA controller drivers do not tolerate non-zero values in
the DMA configuration structures. Zero them to avoid issues with
such DMA controller drivers. Even despite above this is a good
practice per se.

Fixes: 7063c0d9 ("spi/dw_spi: add DMA support")
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Feng Tang <feng.tang@intel.com>
Cc: Feng Tang <feng.tang@intel.com>
Link: https://lore.kernel.org/r/20200506153025.21441-1-andriy.shevchenko@linux.intel.com


Signed-off-by: Mark Brown <broonie@kernel.org>