bugfix: initializing allocated memory for ISR functions

[pintarj]

Allocating dynamic memory for ISR functions using malloc() leaves that memory uninitialized. This causes latter code to perform conditional jumps on uninitialized values. This causes that a GPIO can be randomly marked as already used (which happens in my case).

Output produced while debugging with valgrind:

Conditional jump or move depends on uninitialised value(s)
    at 0x48A8C74: gpioSetISRFunc (orin.c:2044)
    ...

The code that does the conditional jump on an uninitialized value:

if (ISRFunc_CFG[gpio]->gpio != 0) {
    // ...
}

The proposed solution simply uses calloc() instead of malloc(). This causes all the allocated memory to be initialized to 0.

[Rubberazer]

Well spotted and well done, funny how I overlooked this one despite all the testing and stuff. Anyways, many thanks for that and approving your request