vtest: tidy up vtest_resource_busy_wait a bit

Signed-off-by: Chia-I Wu <olvaffe@gmail.com>
Reviewed-by: Ryan Neph <ryanneph@google.com>
Reviewed-by: Gert Wollny <gert.wollny@collabora.com>

vtest/vtest_renderer.c

@@ -1399,24 +1399,18 @@ int vtest_resource_busy_wait(UNUSED uint32_t length_dw)
    /*  handle = bw_buf[VCMD_BUSY_WAIT_HANDLE]; unused as of now */
    flags = bw_buf[VCMD_BUSY_WAIT_FLAGS];
 
-   if (flags == VCMD_BUSY_WAIT_FLAG_WAIT) {
    do {
-         if (renderer.last_fence == (renderer.fence_id - 1)) {
+      busy = renderer.last_fence != (renderer.fence_id - 1);
+      if (!busy || !(flags & VCMD_BUSY_WAIT_FLAG_WAIT))
          break;
-         }
 
+      /* TODO this is bad when there are multiple clients */
       fd = virgl_renderer_get_poll_fd();
       if (fd != -1) {
          vtest_wait_for_fd_read(fd);
       }
-
       virgl_renderer_poll();
-      } while (1);
+   } while (true);
-
-      busy = false;
-   } else {
-      busy = renderer.last_fence != (renderer.fence_id - 1);
-   }
 
    hdr_buf[VTEST_CMD_LEN] = 1;
    hdr_buf[VTEST_CMD_ID] = VCMD_RESOURCE_BUSY_WAIT;