On an UBSAN clang-15 build, if running with UBSAN option
halt_on_error=1 (the issue doesn't show up without it),
MTR fails during mysqld --bootstrap with UBSAN error:

call to function io_callback(tpool::aiocb*) through pointer to incorrect function type 'void (*)(void *)'

This patch corrects the parameter type of io_callback
to match its expected type defined by callback_func,
i.e. (void*).

Reviewed By:
============
<TODO>