pwm: bcm-iproc: Simplify using devm functions

With devm_clk_get_enabled() the call to clk_disable_unprepare() can be
dropped from the error path and the remove callback. With
devm_pwmchip_add() pwmchip_remove() can be dropped. Then the remove
callback is empty and can go away, too.

Also use dev_err_probe() for simplified (and improved) error reporting.

Link: https://lore.kernel.org/r/20230929161918.2410424-2-u.kleine-koenig@pengutronix.de
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>