spi: dw: Initialize n_bytes before the memory barrier

spi: dw: Initialize n_bytes before the memory barrier

Since n_bytes field of the DW SPI private data is also utilized by the
IRQ handler, we need to make sure it' initialization is done before the
memory barrier.

Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Link: https://lore.kernel.org/r/20200920112914.26501-4-Sergey.Semin@baikalelectronics.ru
Signed-off-by: Mark Brown <broonie@kernel.org>