Fix minor unused/uninitialized warnings from GCC 12.3.0

[earlephilhower]

Decorate an unused parameter in the timer API and fill in all structure elements in a PIO API call that generate warnings under GCC 12.

Fixes #1785

[peterharperuk]

Looks good

[kilograham]

An ok - I had wondered if this was a c++ thing - the {0} is valid C but had seen reports of some versions (albeit old) reporting that exact message

[earlephilhower]

I had forgot about that simpler {} solution! Updated with the change and I can confirm no warnings generated for it in the latest G++s.

[lurch]

As this is now a one-character change, it might be worth squashing the commits?

[earlephilhower]

Done, thx!