gpio: gpio-sama5d2-piobu: Demote all kerneldoc headers to basic comment blocks

No attempt has been made to provide proper descriptions for each of
the function arguments throughout the file.  Simply demote all
kerneldoc headers to basic function headers.

Fixes the following W=1 kernel build warnings:

 drivers/gpio/gpio-sama5d2-piobu.c:59: warning: Function parameter or member 'chip' not described in 'sama5d2_piobu_setup_pin'
 drivers/gpio/gpio-sama5d2-piobu.c:59: warning: Function parameter or member 'pin' not described in 'sama5d2_piobu_setup_pin'
 drivers/gpio/gpio-sama5d2-piobu.c:81: warning: Function parameter or member 'chip' not described in 'sama5d2_piobu_write_value'
 drivers/gpio/gpio-sama5d2-piobu.c:81: warning: Function parameter or member 'pin' not described in 'sama5d2_piobu_write_value'
 drivers/gpio/gpio-sama5d2-piobu.c:81: warning: Function parameter or member 'mask' not described in 'sama5d2_piobu_write_value'
 drivers/gpio/gpio-sama5d2-piobu.c:81: warning: Function parameter or member 'value' not described in 'sama5d2_piobu_write_value'
 drivers/gpio/gpio-sama5d2-piobu.c:97: warning: Function parameter or member 'chip' not described in 'sama5d2_piobu_read_value'
 drivers/gpio/gpio-sama5d2-piobu.c:97: warning: Function parameter or member 'pin' not described in 'sama5d2_piobu_read_value'
 drivers/gpio/gpio-sama5d2-piobu.c:97: warning: Function parameter or member 'mask' not described in 'sama5d2_piobu_read_value'
 drivers/gpio/gpio-sama5d2-piobu.c:116: warning: Function parameter or member 'chip' not described in 'sama5d2_piobu_get_direction'
 drivers/gpio/gpio-sama5d2-piobu.c:116: warning: Function parameter or member 'pin' not described in 'sama5d2_piobu_get_direction'
 drivers/gpio/gpio-sama5d2-piobu.c:131: warning: Function parameter or member 'chip' not described in 'sama5d2_piobu_direction_input'
 drivers/gpio/gpio-sama5d2-piobu.c:131: warning: Function parameter or member 'pin' not described in 'sama5d2_piobu_direction_input'
 drivers/gpio/gpio-sama5d2-piobu.c:140: warning: Function parameter or member 'chip' not described in 'sama5d2_piobu_direction_output'
 drivers/gpio/gpio-sama5d2-piobu.c:140: warning: Function parameter or member 'pin' not described in 'sama5d2_piobu_direction_output'
 drivers/gpio/gpio-sama5d2-piobu.c:140: warning: Function parameter or member 'value' not described in 'sama5d2_piobu_direction_output'
 drivers/gpio/gpio-sama5d2-piobu.c:154: warning: Function parameter or member 'chip' not described in 'sama5d2_piobu_get'
 drivers/gpio/gpio-sama5d2-piobu.c:154: warning: Function parameter or member 'pin' not described in 'sama5d2_piobu_get'
 drivers/gpio/gpio-sama5d2-piobu.c:174: warning: Function parameter or member 'chip' not described in 'sama5d2_piobu_set'
 drivers/gpio/gpio-sama5d2-piobu.c:174: warning: Function parameter or member 'pin' not described in 'sama5d2_piobu_set'
 drivers/gpio/gpio-sama5d2-piobu.c:174: warning: Function parameter or member 'value' not described in 'sama5d2_piobu_set'

Signed-off-by: Lee Jones <lee.jones@linaro.org>
Acked-by: Ludovic Desroches <ludovic.desroches@microchip.com>
Cc: Ludovic Desroches <ludovic.desroches@microchip.com>
Cc: Andrei Stefanescu <andrei.stefanescu@microchip.com>
Link: https://lore.kernel.org/r/20200630133345.2232932-6-lee.jones@linaro.org
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>