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>

drivers/spi/spi-bitbang.c

@@ -174,7 +174,7 @@ int spi_bitbang_setup_transfer(struct spi_device *spi, struct spi_transfer *t)
 }
 EXPORT_SYMBOL_GPL(spi_bitbang_setup_transfer);
 
-/**
+/*
  * spi_bitbang_setup - default setup for per-word I/O loops
  */
 int spi_bitbang_setup(struct spi_device *spi)
@@ -208,7 +208,7 @@ int spi_bitbang_setup(struct spi_device *spi)
 }
 EXPORT_SYMBOL_GPL(spi_bitbang_setup);
 
-/**
+/*
  * spi_bitbang_cleanup - default cleanup for per-word I/O loops
  */
 void spi_bitbang_cleanup(struct spi_device *spi)
@@ -427,7 +427,7 @@ int spi_bitbang_start(struct spi_bitbang *bitbang)
 }
 EXPORT_SYMBOL_GPL(spi_bitbang_start);
 
-/**
+/*
  * spi_bitbang_stop - stops the task providing spi communication
  */
 void spi_bitbang_stop(struct spi_bitbang *bitbang)