devel/build_chroot: fix typo id DIST_RELEASE conditional

Dispatch on the value of the DIST_RELEASE variable,
not its name.

Signed-off-by: Gerard Oskamp <gjo@google.com>
Signed-off-by: Klaus Aehlig <aehlig@google.com>
Reviewed-by: Petr Pudlak <pudlak@google.com>