Suppress Coverity complaints in readfuncs.c.

Coverity is complaining that the value returned by pg_strtok in
READ_LOCATION_FIELD and READ_BITMAPSET_FIELD macros is not used. In commit
39bfc94c, we did this to the other macros
to placate compilers that complained when the variable was completely
unused, this extends that to the last remaining macros.