Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "Docs: test case description for TC080 and TC081"
  - Docs: test case description for TC080 and TC081

    JIRA: YARDSTICK-825

    Change-Id: Ib2f8d0b88378c0dd0bd20ba38141a205fa7ae486
    Signed-off-by: JingLu5 <lvjing5@huawei.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index 3e27c93..3d51fd0 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit 3e27c93dbe3cd117df0743a65644e94e859d6fa4
+Subproject commit 3d51fd0ac37c2df1c72f7a2dcff2ec9c88196043