rocksdb: sync with upstream

to pickup the change removing "add_definitions(-DROCKSDB_JEMALLOC)" in
rocksdb's CMakeListst.txt, so FreeBSD can built without the jemalloc's
header files.

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

diff --git a/src/rocksdb b/src/rocksdb
index 3b4ac8076bff9fd6a8b4ccbc37a1995d08981840..9f2cc59ec5065c828dabbab483506bde681c955c 160000 (submodule)
--- a/src/rocksdb
+++ b/src/rocksdb
@@ -1 +1 @@
-Subproject commit 3b4ac8076bff9fd6a8b4ccbc37a1995d08981840
+Subproject commit 9f2cc59ec5065c828dabbab483506bde681c955c