spi: bitbang: Don't call chipselect() in spi_bitbang_setup()

spi_setup() already call spi_set_cs() right after calling the
controller setup method, so there is no need for the bitbang driver to
do that. Because of this the chipselect() callback was confusingly
still called when CS is GPIO based.

Signed-off-by: Alban Bedel <albeu@free.fr>
Signed-off-by: Mark Brown <broonie@kernel.org>