spi: remove spi_set_cs_timing()

No one seems to be using this global and exported function, so remove it
as it is no longer needed.

Cc: Mark Brown <broonie@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/20210609071918.2852069-1-gregkh@linuxfoundation.org


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