rocksdb: do not use aligned_alloc

this change picks up the change to "use posix_memalign() for
aligned_alloc()" in ceph/rocksdb.

Fixes: http://tracker.ceph.com/issues/23653
Signed-off-by: Kefu Chai <kchai@redhat.com>

diff --git a/src/rocksdb b/src/rocksdb
index 5ec382b918f41481c089a45fb3d8472c017589fc..f4a857da0b720691effc524469f6db895ad00d8e 160000 (submodule)
--- a/src/rocksdb
+++ b/src/rocksdb
@@ -1 +1 @@
-Subproject commit 5ec382b918f41481c089a45fb3d8472c017589fc
+Subproject commit f4a857da0b720691effc524469f6db895ad00d8e