pinctrl: sx150x: use correct registers for reg_sense (sx1502 and sx1508)

All other registers on these chips are 8-bit, but reg_sense is 16-bits
and therefore needs to be moved down one notch.
This was apparently overlooked in the conversion to regmap, which only
updated the register locations for the 16-bit chips.

Fixes: 6489677f ("pinctrl-sx150x: Replace sx150x_*_cfg by means of regmap API")
Signed-off-by: Peter Rosin <peda@axentia.se>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>