virDomainFormatSchedDef: Initialize @priority

Older gcc fails to see that the variable is set iff @hasPriority
== true in which case the former is set a value. Initialize the
value while declaring it to make the compiler shut up.
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>

src/conf/domain_conf.c

@@ -21472,7 +21472,7 @@ virDomainFormatSchedDef(virDomainDefPtr def,
             virBitmapPtr currentMap = NULL;
             ssize_t nextprio;
             bool hasPriority = false;
-            int priority;
+            int priority = 0;
 
             switch ((virProcessSchedPolicy) i) {
             case VIR_PROC_POLICY_NONE: