block/graph-lock: fix missed wakeup in bdrv_graph_co_rdunlock()

Make aio_wait_kick() unconditional in bdrv_graph_co_rdunlock().
bdrv_graph_wrlock() zeroes has_writer while polling, so rdunlock
cannot rely on has_writer to detect a waiting writer. The kick is
a no-op when no one is waiting.

Cherry-picked from upstream stable-11.0 commit fddafa15a9.

Signed-off-by: Jason Truong <jason.truong@windriver.com>

Author: hungmtruong

block/graph-lock.c

@@ -277,12 +277,6 @@ void coroutine_fn bdrv_graph_co_rdunlock(void)
     /* make sure writer sees reader_count before we check has_writer */
     smp_mb();
 
-    /*
-     * has_writer == 0: this means reader will read reader_count decreased
-     * has_writer == 1: we don't know if writer read reader_count old or
-     *                  new. Therefore, kick again so on next iteration
-     *                  writer will for sure read the updated value.
-     */
     /*
      * Always kick: bdrv_graph_wrlock() zeroes has_writer while polling (to
      * let callbacks take the reader lock via the fast path), so we cannot