FYI: add explicit success returncode to mkbc.c

[Xerxes Rånby]

I have made a trivial change that makes mkbc.c explicitly return 0 on
success.
When using mkbc in cross compile setups then the tool could return a non
zero return code value and break the build. By explicitly returning 0
fixes it.

commited to:
http://icedtea.classpath.org/hg/icedtea6/rev/3e6dd786e038

Cheers
Xerxes