ensure fd initialized

New upstream yocto enforces stricter compile rules. Without this commit,
we get this error:

| ../git/oem/ibm/libpldmresponder/utils.cpp:62:9: error: 'fd' may be used uninitialized in this function [-Werror=maybe-uninitialized]
|    62 |     int fd;
|       |
| cc1plus: all warnings being treated as errors

Signed-off-by: Andrew Geissler <geissonator@yahoo.com>
Change-Id: Ie089dfbede0361963a90828ce6826e324285b50d