Adjust wording of two fall-through comments

[Florian Weimer]

* Joseph Myers:

> 	* iconvdata/cns11643.h (ucs4_to_cns11643): Adjust fall-through
> 	comment wording.
> 	* nis/nis_call.c (__do_niscall3): Likewise.

Looks okay to me.

Thanks,
Florian