gpio: mcp23s08: fix casting caused build warning
gpio: mcp23s08: fix casting caused build warning

Signed-off-by: SeongJae Park <4e244449b52bf6ddddd07d261eea0e61e60df45e@gmail.com>
Signed-off-by: Linus Walleij <9cd9d802d23c0ed5e224beabf4ae4a5c478746ef@linaro.org>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs