kconfig: add unexpected data itself to warning

If the .config parser runs into unexpected data it emits warnings like:
    .config:6911:warning: unexpected data

Add the unexpected data itself to this warning. That makes it easier to
discover what is actually going wrong:
     .config:6911:warning: unexpected data: CONFOG_CHARGER_TPS65217=m

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Signed-off-by: Michal Marek <mmarek@suse.com>
Signed-off-by: Christian Lamparter <chunkeey@gmail.com>