nodedev: fix a uninitialized variable build failure

Fix a -Werror=maybe-uninitialized warning
Signed-off-by: NChen Hanxiao <chenhanxiao@cn.fujitsu.com>
Signed-off-by: NEric Blake <eblake@redhat.com>

src/conf/node_device_conf.c

@@ -1349,7 +1349,7 @@ virNodeDevCapsDefParseXML(xmlXPathContextPtr ctxt,
 {
     virNodeDevCapsDefPtr caps;
     char *tmp;
-    int val, ret;
+    int val, ret = -1;
 
     if (VIR_ALLOC(caps) < 0)
         return NULL;