Fix \param names in interp_get_base and riscv_timer_set_mtimecmp - #3165

Doxygen drops unmatched names quietly

Well that's a bit annoying 🙁

I was wrong about that. It does warn, I just checked with 1.18 against the defaults docs/Doxyfile.in inherits:

t.h:2: warning: argument 'lane' of command @param is not found in the argument list of interp_get_base(void *interp, unsigned index)
t.h:2: warning: The following parameter of interp_get_base(void *interp, unsigned index) is not documented:
  parameter 'index'

Both of those, and then it exits 0. So the docs job stays green and the two lines scroll past with everything else. WARN_AS_ERROR = FAIL_ON_WARNINGS in docs/Doxyfile.in would catch the next one without changing how much output you get, it runs the whole build and only sets the exit code at the end.