debian: depend on libosmo-sigtran-dev, not libosmo-sccp-dev

We recently fixed package naming / sub-packagign in the libosmo-sccp
git repository, so now we need to depend on the proper package name.

Change-Id: I6e4f8fa96e5f39f988d6993ba3931cb7df70e905
diff --git a/debian/control b/debian/control
index 56a7667..bc9b221 100644
--- a/debian/control
+++ b/debian/control
@@ -14,7 +14,7 @@
                libosmo-netif-dev,
                libosmocore-dev,
                libosmo-netif-dev,
-               libosmo-sccp-dev,
+               libosmo-sigtran-dev (>= 0.8.0),
                python (>= 2.7)
 Standards-Version: 3.9.8
 Vcs-Git: git://git.osmocom.org/osmo-iuh.git