pinctrl: lpc18xx: fix schmitt trigger setup

The param_val variable is what determines if schmitt
trigger is enabled on a pin or not. A typo here mean
that schmitt trigger was always enabled for standard
and i2c pins.

Signed-off-by: Joachim Eastwood <manabian@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>