None of the in-tree instantiations of struct t7l66xb_platform_data
provides a disable callback. So better don't dereference this function
pointer unconditionally. As there is no user, drop it completely instead
of calling it conditional.

This is a preparation for making platform remove callbacks return void.

Fixes: 1f192015 ("mfd: driver for the T7L66XB TMIO SoC")
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/20220530192430.2108217-3-u.kleine-koenig@pengutronix.de