Git BranchAddDialog: small fixes

Change-Id: I99910fdb3a646ad818ad58103beb5f63de57ec18
Reviewed-by: Orgad Shaneh <orgads@gmail.com>
Reviewed-by: André Hartmann <aha_1980@gmx.de>
Reviewed-by: Tobias Hunger <tobias.hunger@qt.io>

src/plugins/git/branchadddialog.h

@@ -46,7 +46,7 @@ public:
 
     void setTrackedBranchName(const QString &name, bool remote);
 
-    bool track();
+    bool track() const;
 
 private:
     void updateButtonStatus();