config_file: enhance parsing boolean "readonly" key
config_file: enhance parsing boolean "readonly" key

Return an error instead of interpreting a typo in the readonly key's value as
"false".

Signed-off-by: Ulrich Ölmann <dd989c3d4b9e0c1c162946243f1ca35d034a3035@pengutronix.de>

ejoerns/rauc,jluebbe/rauc,ejoerns/rauc,ejoerns/rauc,jluebbe/rauc,rauc/rauc,jluebbe/rauc,rauc/rauc,rauc/rauc