Fix the recent CI build failures

After commits e2087c29 and ec0793de older GCC started act very smart and
complain about potentially uninitialized variable, which existed prior
to these patches + even if the affected vars were left uninitialized the
function responsible for filling them in would have failed with NULL
being returned which the caller has always handled carefully.
Although GCC complained only about a single variable, let's initialize
all of them so as to prevent any further potential breakages.
Signed-off-by: NErik Skultety <eskultet@redhat.com>

src/conf/domain_conf.c

@@ -18400,9 +18400,9 @@ virDomainThreadSchedParseHelper(xmlNodePtr node,
                                 virDomainDefPtr def)
 {
     ssize_t next = -1;
-    virDomainThreadSchedParamPtr sched;
-    virProcessSchedPolicy policy;
-    int priority;
+    virDomainThreadSchedParamPtr sched = NULL;
+    virProcessSchedPolicy policy = 0;
+    int priority = 0;
     VIR_AUTOPTR(virBitmap) map = NULL;
 
     if (!(map = virDomainSchedulerParse(node, name, &policy, &priority)))