Fix -Wimplicit-function-declaration compilation warning by moving libgeom.h
#include below the stdio.h #include.

gctl_dump(3) needs stdio.h, per reasoning noted in r317289.

MFC after: 5 weeks
PR: 218809
Submitted by: Chang-Hsien Tsai <luke.tw@gmail.com>
Sponsored by: Dell EMC Isilon