pwm: renesas-tpu: Make use of devm functions

This simplifies an error path in .probe() and allows to drop the .remove()
function.

Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>