dmclock: pick up change to support seastar

so if WITH_SEASTAR is defined, the POSIX synchronous primitives
are either replaced with seastar counterparts or disabled.

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

diff --git a/src/dmclock b/src/dmclock
index 97db58038d941df70af5b2c39169fe57d0818460..e4ccdcfa828c84b8ea775a928118f2b8012d0f42 160000 (submodule)
--- a/src/dmclock
+++ b/src/dmclock
@@ -1 +1 @@
-Subproject commit 97db58038d941df70af5b2c39169fe57d0818460
+Subproject commit e4ccdcfa828c84b8ea775a928118f2b8012d0f42