mfd: ti_am335x_tscadc: Update logic in CTRL register for 5-wire TS

The logic in AFE_Pen_Ctrl bitmask in the CTRL register is different for five
wire versus four or eight wire touschscreens. This patch should fix this for
five-wire touch screens. There should be no change needed here for four and
eight wire tousch screens.

Signed-off-by: Jeff Lance <j-lance1@ti.com>
[bigeasy: keep the change mfd only]
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Lee Jones <lee.jones@linaro.org>