mm-origin: Explicitly cast ussd state

This is better than the implicit conversion of the enum.

plugins/provider/mm/calls-mm-origin.c

@@ -191,7 +191,7 @@ calls_mm_ussd_get_state (CallsUssd *ussd)
   if (!self->ussd)
     return CALLS_USSD_STATE_UNKNOWN;
 
-  return mm_modem_3gpp_ussd_get_state (self->ussd);
+  return (CallsUssdState) mm_modem_3gpp_ussd_get_state (self->ussd);
 }
 
 static void

src/calls-ussd.h

@@ -32,6 +32,7 @@ G_BEGIN_DECLS
 
 G_DECLARE_INTERFACE (CallsUssd, calls_ussd, CALLS, USSD, GObject)
 
+/* This is basically MMModem3gppUssdSessionState */
 typedef enum
 {
   CALLS_USSD_STATE_UNKNOWN,