fix CONFIG_QEMU_HELPERDIR generation again commit 38f419f35225 fixed a breakage with CONFIG_QEMU_HELPERDIR which has been introduced by 8bf188aa18ef7a8. But while techinically that fix has been correct, all other similar variables are handled differently. Make it consistent, and let scripts/create_config expand and capitalize the variable properly like for all other qemu_*dir variables. Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>