tools: gpio: Fix several incorrect format specifiers

Make a minor change to eliminate static checker warnings. The variable
lines[] is unsigned, so the correct format specifier should be %u
instead of %d.

Signed-off-by: Luo Yifan <luoyifan@cmss.chinamobile.com>
Link: https://lore.kernel.org/r/20241113021458.291252-1-luoyifan@cmss.chinamobile.com


Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>