pinctrl: mcp23s08: Reset all pins to input at probe

pinctrl: mcp23s08: Reset all pins to input at probe

At startup, the driver just assumes that all registers have their
default values. But after a soft reset, the chip will just be in the
state it was, and some pins may have been configured as outputs. Any
modification of the output register will cause these pins to be driven
low, which leads to unexpected/unwanted effects. To prevent this from
happening, set the chip's IO configuration register to a known safe
mode (all inputs) before toggling any other bits.

Signed-off-by: Mike Looijmans <mike.looijmans@topic.nl>
Link: https://lore.kernel.org/20250314151803.28903-1-mike.looijmans@topic.nl
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>