Adjust wording of two fall-through comments.

In two places in glibc, -Wextra produces implicit-fallthrough warnings
where there are comments about the fall-through but their wording
doesn't match one of the forms expected by the default
implicit-fallthrough level.  This patch adjusts those two places to
have a comment in a form that is accepted, so avoiding the warning
(this seems preferable to only being able to use a looser level of the
warning that allows any comment at all as evidence of deliberate
fall-through).

Tested for x86_64.

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