fix: project/reference submodule hash

Restore project/reference submodule hierarchy after merging [1] which
wasn't rebased on latest master commit. [1] had f0996a5476ae89 as parent
commit. Eventually [1] must have [2] as parent commit.

[1] https://git.trustedfirmware.org/hafnium/project/reference.git/commit/?id=89ee8cc5c373889ee93ac38c35f3544e1966de83
[2] https://git.trustedfirmware.org/hafnium/project/reference.git/commit/?id=25dc72a357f077e1f532e7bc8a45d6749f8367e9

Change-Id: I6a697e7ca6c3b9ec6c5b649968c6de1d76766a3f
Signed-off-by: Olivier Deprez <olivier.deprez@arm.com>
diff --git a/project/reference b/project/reference
index eb411ea..89ee8cc 160000
--- a/project/reference
+++ b/project/reference
@@ -1 +1 @@
-Subproject commit eb411ea7c3b0ed1ab057b1389f4b443896ad7495
+Subproject commit 89ee8cc5c373889ee93ac38c35f3544e1966de83