pwm: jz4740: Make use of devm_pwmchip_alloc() function

This prepares the pwm-jz4740 driver to further changes of the pwm core
outlined in the commit introducing devm_pwmchip_alloc(). There is no
intended semantical change and the driver should behave as before.

Acked-by: Paul Cercueil <paul@crapouillou.net>
Link: https://lore.kernel.org/r/14a081c097b4e7c7f346ca6557ece8d16ad5749d.1707900770.git.u.kleine-koenig@pengutronix.de


Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>