mfd: twl: Remove platform data support

There is no in-tree machine that provides a struct twl4030_platform_data
since commit e92fc4f0 ("ARM: OMAP2+: Drop legacy board file for
LDP"). So assume dev_get_platdata() returns NULL in twl_probe() and
simplify accordingly.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20220614152148.252820-1-u.kleine-koenig@pengutronix.de