Shrink boot2 a bit more by factoring out common pattern
of printf();return(-1);

This shrinks it by 8bytes using clang35 and by 12bytes using clang34.


git-svn-id: svn+ssh://svn.freebsd.org/base/head@275237 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f