spi: dw: Discard dma_width member of the dw_spi structure

This member has exactly the same value as n_bytes of the DW SPI private
data object, it's calculated at the same point of the transfer method,
n_bytes isn't changed during the whole transfer, and they even serve for
the same purpose - keep number of bytes per transfer word, though the
dma_width is used only to calculate the DMA source/destination addresses
width, which n_bytes could be also utilized for. Taking all of these
into account let's replace the dma_width member usage with n_bytes one
and remove the former.

Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Georgy Vlasov <Georgy.Vlasov@baikalelectronics.ru>
Cc: Ramil Zaripov <Ramil.Zaripov@baikalelectronics.ru>
Cc: Alexey Malahov <Alexey.Malahov@baikalelectronics.ru>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: Paul Burton <paulburton@kernel.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: linux-mips@vger.kernel.org
Cc: devicetree@vger.kernel.org

Link: https://lore.kernel.org/r/20200522000806.7381-6-Sergey.Semin@baikalelectronics.ru
Signed-off-by: Mark Brown <broonie@kernel.org>