async: Use bool for boolean struct members and remove a hole

Using bool reduces the size of the structure and improves readability.
A hole in the structure was removed.

Signed-off-by: Stefan Weil <sw@weilnetz.de>
Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>

async.c

@@ -35,10 +35,10 @@ static struct QEMUBH *first_bh;
 struct QEMUBH {
     QEMUBHFunc *cb;
     void *opaque;
-    int scheduled;
-    int idle;
-    int deleted;
     QEMUBH *next;
+    bool scheduled;
+    bool idle;
+    bool deleted;
 };
 
 QEMUBH *qemu_bh_new(QEMUBHFunc *cb, void *opaque)