Fix the references to the ets_update_cpu_frequency_rom ROM function

[jessebraham]

Closes #367 (I think 😁). It was already working on this system to begin with, I'll hop on my other computer in a bit and test it out there.

[bjoernQ]

LGTM

Should do the trick - I guess we should call that on other targets as well since otherwise ROM functions like ets_delay won't work correctly but that's something for another day

[jessebraham]

Tested on my other system and this seems to have resolved the linker error.