libosmo-mgcp-client: Don't link libosmogsm, but link libosmovty

This addresses the following dpkg-shlibdeps warnings:

Change-Id: I737c36402b7b88634b56725f2caab4f5f971ac51
dpkg-shlibdeps: warning: symbol install_element used by debian/libosmo-mgcp-client0/usr/lib/x86_64-linux-gnu/libosmo-mgcp-client.so.0.0.0 found in none of the libraries
dpkg-shlibdeps: warning: symbol vty_out used by debian/libosmo-mgcp-client0/usr/lib/x86_64-linux-gnu/libosmo-mgcp-client.so.0.0.0 found in none of the libraries
1 file changed