pwm: tiecap: Simplify using devm_pwmchip_add()

With devm_pwmchip_add() there is no need to explicitly call
pwmchip_remove(), so this call can be dropped from the remove callback.

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