libosmo-mgcp: Don't link against libosmogsm; link against libosmovty

This addresses the following dpkg-shlibdeps warnings:

Change-Id: I518eb5e19cef5f261711b034d28337265c69f443
dpkg-shlibdeps: warning: symbol install_element_ve used by debian/libosmo-mgcp0/usr/lib/x86_64-linux-gnu/libosmo-mgcp.so.0.0.0 found in none of the libraries
dpkg-shlibdeps: warning: symbol vty_read_config_file used by debian/libosmo-mgcp0/usr/lib/x86_64-linux-gnu/libosmo-mgcp.so.0.0.0 found in none of the libraries
dpkg-shlibdeps: warning: symbol vty_install_default used by debian/libosmo-mgcp0/usr/lib/x86_64-linux-gnu/libosmo-mgcp.so.0.0.0 found in none of the libraries
dpkg-shlibdeps: warning: symbol install_element used by debian/libosmo-mgcp0/usr/lib/x86_64-linux-gnu/libosmo-mgcp.so.0.0.0 found in none of the libraries
dpkg-shlibdeps: warning: symbol install_node used by debian/libosmo-mgcp0/usr/lib/x86_64-linux-gnu/libosmo-mgcp.so.0.0.0 found in none of the libraries
dpkg-shlibdeps: warning: symbol vty_out used by debian/libosmo-mgcp0/usr/lib/x86_64-linux-gnu/libosmo-mgcp.so.0.0.0 found in none of the libraries
dpkg-shlibdeps: warning: symbol argv_concat used by debian/libosmo-mgcp0/usr/lib/x86_64-linux-gnu/libosmo-mgcp.so.0.0.0 found in none of the libraries
diff --git a/src/libosmo-mgcp/Makefile.am b/src/libosmo-mgcp/Makefile.am
index e121fea..a9e1b6c 100644
--- a/src/libosmo-mgcp/Makefile.am
+++ b/src/libosmo-mgcp/Makefile.am
@@ -14,7 +14,7 @@
 
 AM_LDFLAGS = \
 	$(LIBOSMOCORE_LIBS) \
-	$(LIBOSMOGSM_LIBS) \
+	$(LIBOSMOVTY_LIBS) \
 	$(LIBOSMONETIF_LIBS) \
 	$(COVERAGE_LDFLAGS) \
 	$(NULL)