spi: dw: Replace spi->chip_select references with function calls

spi: dw: Replace spi->chip_select references with function calls

New set/get APIs for accessing spi->chip_select were introduced by
'commit 9e264f3f85a5 ("spi: Replace all spi->chip_select and spi->cs_gpiod
references with function call")', but the 'commit 2c8606040a80 ("spi: dw:
Add support for AMD Pensando Elba SoC")' uses the old interface by directly
accessing spi->chip_select. So, replace all spi->chip_select references
in the driver with new get/set APIs.

Signed-off-by: Amit Kumar Mahapatra <amit.kumar-mahapatra@amd.com
Acked-by: Serge Semin <fancer.lancer@gmail.com
Link: https://lore.kernel.org/r/20230515130343.63770-1-amit.kumar-mahapatra@amd.com
Signed-off-by: Mark Brown <broonie@kernel.org