util: Fix uninitalized variable to avoid garbage

This commit fixes an unitialized variable to avoid garbage value
when virNetDevBridgeGet method returns error. When, that method fails
before initialize 'val' variable, it can cause problems related to
that.
Signed-off-by: NJulio Faracco <jcfaracco@gmail.com>
Reviewed-by: NErik Skultety <eskultet@redhat.com>

src/util/virnetdevbridge.c

@@ -760,7 +760,7 @@ int virNetDevBridgeGetSTP(const char *brname,
                           bool *enabled)
 {
     int ret = -1;
-    unsigned long val;
+    unsigned long val = 0;
 
     ret = virNetDevBridgeGet(brname, "stp_state", &val);
     *enabled = val ? true : false;