gpio.h Gpio_t pinIndex is only 16-bit, which only allows for 16 pins per port

[Cjtechnologyltd]

Hello, I had to edit gpio.h for my microcontroller (Maxim MX32670) which has 32 gpios per port.

As such, I had to edit the variable type of "pinIndex" within Gpio_t to be uint32_t instead of uint16_t.

Please consider making this change to improve compatibility.