spi: spi-bitbang: Demote obvious misuse of kerneldoc to standard comment blocks

No attempt has been made to document any of the demoted functions here.

Fixes the following W=1 kernel build warning(s):

 drivers/spi/spi-bitbang.c:181: warning: Function parameter or member 'spi' not described in 'spi_bitbang_setup'
 drivers/spi/spi-bitbang.c:215: warning: Function parameter or member 'spi' not described in 'spi_bitbang_cleanup'
 drivers/spi/spi-bitbang.c:434: warning: Function parameter or member 'bitbang' not described in 'spi_bitbang_stop'

Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20200717135424.2442271-3-lee.jones@linaro.org


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