This patch converts descriptions of the structures defined in
linux/gpio_keys.h to follow kernel-doc format.

There is no functional change.
Signed-off-by: NAndy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: NLinus Walleij <linus.walleij@linaro.org>
Signed-off-by: NDmitry Torokhov <dmitry.torokhov@gmail.com>