tools: gpio-utils: fix various kernel-doc warnings

Fix several problems in kernel-doc notation in gpio-utils.c.

gpio-utils.c:37: warning: Incorrect use of kernel-doc format:  * gpiotools_request_line() - request gpio lines in a gpiochip
gpio-utils.c:61: warning: expecting prototype for doc(). Prototype was for gpiotools_request_line() instead
gpio-utils.c:265: warning: Excess function parameter 'value' description in 'gpiotools_sets'
gpio-utils.c:1: warning: 'gpiotools_request_lines' not found

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: linux-gpio@vger.kernel.org
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>