kbuild: don't warn about include/linux/version.h not including itself

This patch makes checkversion.pl not warn that include/linux/version.h
dosen't include itself.

Signed-off-by: Peter Foley <pefoley2@verizon.net>
[mmarek: simplified to use 'next if' syntax]
Signed-off-by: Michal Marek <mmarek@suse.cz>