spi: spi-davinci: Fix a few kerneldoc misspellings and API slippages

spi: spi-davinci: Fix a few kerneldoc misspellings and API slippages

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

 drivers/spi/spi-davinci.c:249: warning: Function parameter or member 'dspi' not described in 'davinci_spi_get_prescale'
 drivers/spi/spi-davinci.c:249: warning: Function parameter or member 'max_speed_hz' not described in 'davinci_spi_get_prescale'
 drivers/spi/spi-davinci.c:249: warning: Excess function parameter 'maxspeed_hz' description in 'davinci_spi_get_prescale'
 drivers/spi/spi-davinci.c:719: warning: Function parameter or member 'data' not described in 'dummy_thread_fn'
 drivers/spi/spi-davinci.c:719: warning: Excess function parameter 'context_data' description in 'dummy_thread_fn'
 drivers/spi/spi-davinci.c:735: warning: Function parameter or member 'data' not described in 'davinci_spi_irq'
 drivers/spi/spi-davinci.c:735: warning: Excess function parameter 'context_data' description in 'davinci_spi_irq'

Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20200717135424.2442271-4-lee.jones@linaro.org
Signed-off-by: Mark Brown <broonie@kernel.org>