block/stream: Remove redundant statement in stream_run()

Clang static code analyzer show warning:
  block/stream.c:186:9: warning: Value stored to 'ret' is never read
        ret = 0;
        ^     ~
Reported-by: Euler Robot <euler.robot@huawei.com>
Signed-off-by: Chen Qun <kuhn.chenqun@huawei.com>
Reviewed-by: John Snow <jsnow@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20200302130715.29440-3-kuhn.chenqun@huawei.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>

block/stream.c

@@ -114,7 +114,6 @@ static int coroutine_fn stream_run(Job *job, Error **errp)
     int64_t offset = 0;
     uint64_t delay_ns = 0;
     int error = 0;
-    int ret = 0;
     int64_t n = 0; /* bytes */
 
     if (bs == s->bottom) {
@@ -139,6 +138,7 @@ static int coroutine_fn stream_run(Job *job, Error **errp)
 
     for ( ; offset < len; offset += n) {
         bool copy;
+        int ret;
 
         /* Note that even when no rate limit is applied we need to yield
          * with no pending I/O here so that bdrv_drain_all() returns.
@@ -183,7 +183,6 @@ static int coroutine_fn stream_run(Job *job, Error **errp)
                 break;
             }
         }
-        ret = 0;
 
         /* Publish progress */
         job_progress_update(&s->common.job, n);