mfd: tc6387xb: Drop disable callback that is never called

The driver never calls the disable callback, so drop the member from
the platform struct and all callbacks from the actual platform datas.

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/20220530192430.2108217-4-u.kleine-koenig@pengutronix.de