pwm: pca9685: Use gpio core provided macro GPIO_LINE_DIRECTION_OUT

GPIO core recently added macro to uniformly specify direction of a GPIO
line, so use it.

Signed-off-by: Rishi Gupta <gupt21@gmail.com>
Acked-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>