Fix: Set data to NULL in drivers

drivers/atmodem/call-volume.c

@@ -210,6 +210,8 @@ static void at_call_volume_remove(struct ofono_call_volume *cv)
 {
 	struct cv_data *cvd = ofono_call_volume_get_data(cv);
 
+	ofono_call_volume_set_data(cv, NULL);
+
 	g_free(cvd);
 }
 

drivers/atmodem/network-registration.c

@@ -712,6 +712,8 @@ static void at_netreg_remove(struct ofono_netreg *netreg)
 {
 	struct netreg_data *nd = ofono_netreg_get_data(netreg);
 
+	ofono_netreg_set_data(netreg, NULL);
+
 	g_free(nd);
 }
 

drivers/atmodem/phonebook.c

@@ -535,6 +535,8 @@ static void at_phonebook_remove(struct ofono_phonebook *pb)
 	if (pbd->old_charset)
 		g_free(pbd->old_charset);
 
+	ofono_phonebook_set_data(pb, NULL);
+
 	g_free(pbd);
 }
 

drivers/atmodem/voicecall.c

@@ -961,6 +961,9 @@ static void at_voicecall_remove(struct ofono_voicecall *vc)
 
 	g_slist_foreach(vd->calls, (GFunc) g_free, NULL);
 	g_slist_free(vd->calls);
+
+	ofono_voicecall_set_data(vc, NULL);
+
 	g_free(vd);
 }