spi: rspi: Remove set_config_register() macro

The set_config_register() macro is used in a single place.
Make the code easier to read by just removing it.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20200102133822.29346-5-geert+renesas@glider.be


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