debian/control: correct library dependency of osmo-mgw against libosmo-mgcp1

When the library version was bump, the dependency of osmo-mgw
was forgotten.

Change-Id: I3eeafa3c294d9ec71a72fb2833fe3b2bdef05a50
Fixes: e7d27aeae10b ("Tag/Release Version 1.2.0")
1 file changed