configure.ac/debian: Require libosmo-mgcp-client-dev >= 1.2.0

We recently started to use some symbols that were not available in
libosmo-mgcp-client-dev 1.0.0 or even 1.1.0.  Let's depend on a newly
tagged version of libosmo-mgcp-client.

Change-Id: Ic5d3add1c69181aabbdb684a01a6ba7bcea1fe2c
diff --git a/debian/control b/debian/control
index 963d664..5e9ad60 100644
--- a/debian/control
+++ b/debian/control
@@ -18,7 +18,7 @@
                libosmo-abis-dev (>= 0.3.2),
                libosmo-netif-dev (>= 0.1.0),
                libosmo-legacy-mgcp-dev (>= 1.0.0),
-               libosmo-mgcp-client-dev (>= 1.0.0)
+               libosmo-mgcp-client-dev (>= 1.2.0)
 Standards-Version: 3.9.8
 Vcs-Git: git://git.osmocom.org/osmo-bsc.git
 Vcs-Browser: https://git.osmocom.org/osmo-bsc/