ensure variable initialized and error path reported

New upstream yocto brings in an option that ensure all variables are
initialized. Without this change, we get this failure:

| ../git/libpldmresponder/bios_integer_attribute.cpp:158:12: error:
|   'value' may be used uninitialized in this function [-Werror=maybe-uninitialized]
|   158 |     return value;
|       |            ^~~~~
| cc1plus: all warnings being treated as errors

There's no good way to report a property type is not found so add code
to raise an exception in this situation.

Signed-off-by: Andrew Geissler <geissonator@yahoo.com>
Change-Id: Ie218f72b6d58fa4ad1e99f1a83eb17f3f87cd941