cml1.bbclass: do_diffconfig: Don't override .config with .config.orig

cml1.bbclass: do_diffconfig: Don't override .config with .config.orig

Fixed:
1) $ bitbake virtual/kernel -cmenuconfig
Do some changes and save the new config to default .config.
2) $ bitbake virtual/kernel -cdiffconfig
The config fragment is dumped into ${WORKDIR}/fragment.cfg.

But the .config which was saved by step #1 is overridden by .config.orig, so
the changes will be lost if run 'bitbake virtual/kernel'

And the following comment is for subprocess.call(), not for shutil.copy(),
so move subprocess.call() to the correct location.
    # No need to check the exit code as we know it's going to be
    # non-zero, but that's what we expect.

Signed-off-by: Robert Yang <liezhi.yang@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>