stream: fix ratelimit_set_speed

The formula to compute slice_quota was wrong since commit 6ef228fc.
Signed-off-by: NDietmar Maurer <dietmar@proxmox.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

include/qemu/ratelimit.h

@@ -42,7 +42,7 @@ static inline void ratelimit_set_speed(RateLimit *limit, uint64_t speed,
                                        uint64_t slice_ns)
 {
     limit->slice_ns = slice_ns;
-    limit->slice_quota = ((double)speed * 1000000000ULL) / slice_ns;
+    limit->slice_quota = ((double)speed * slice_ns)/1000000000ULL;
 }
 
 #endif