rocksdb: sync with upstream

to pick up
- bug fixes since 5.8.0
- crc32c_3way introduced in 5.9.0 for better performance on platforms
with PCLMULQDQ support.
- the fixes for silencing the fallthrough warnings when compiling with
GCC-7

for detailed changelog since 5.8.0, see
https://github.com/facebook/rocksdb/blob/master/HISTORY.md

Signed-off-by: Kefu Chai <kchai@redhat.com>

diff --git a/src/rocksdb b/src/rocksdb
index 8dd0a7e11abad6bc32e59a5cba8769961e085312..5ec382b918f41481c089a45fb3d8472c017589fc 160000 (submodule)
--- a/src/rocksdb
+++ b/src/rocksdb
@@ -1 +1 @@
-Subproject commit 8dd0a7e11abad6bc32e59a5cba8769961e085312
+Subproject commit 5ec382b918f41481c089a45fb3d8472c017589fc