sim/erc32: Use int32_t as IRQ callback argument

sim/erc32: Use int32_t as IRQ callback argument

Clang generates a warning if an argument is passed to a function without
prototype (zero arguments, even without (void)).  Such calls are deprecated
forms of indefinite arguments passing ("-Wdeprecated-non-prototype").
On the default configuration, it (somehow) doesn't cause a build failure but
a warning is generated.

But because the cause is the same as the issue the author fixed in
"sim/erc32: Use int32_t as event callback argument", it would be better to
fix it now to prevent problems in the future.

To fix the issue, this commit makes struct irqcall to use int32_t as a
callback (callback) argument of an IRQ.