input: ti_am33x_tsc: remove unwanted fifo flush

When touchscreen and ADC are used together, this
unwanted fifo flush leads to loss of ADC data.

Signed-off-by: Patil, Rachna <rachna@ti.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>