input: ti_am33x_tsc: remove platform_data support

This patch removes access to platform data mfd_tscadc_board because the
platform is DT only.

Acked-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>