spi: spi-fsl-dspi: Fix cs_change handling in message transfer

There are use cases when chip select should be triggered between transfers
in single SPI message. Current implementation does this only on last
transfer in message ignoring cs_change value provided in current transfer.

Signed-off-by: Andrey Vostrikov <andrey.vostrikov@cogentembedded.com>
Signed-off-by: Mark Brown <broonie@kernel.org>