pwm: clps711x: Simplify using devm_pwmchip_add()

With devm_pwmchip_add() we can drop pwmchip_remove() from the device
remove callback. The latter can then go away, too and as this is the
only user of platform_get_drvdata(), the respective call to
platform_set_drvdata() can go, too.

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