KitInformation: Make defaultValue take a const Kit *

There is no reason not to.

Change-Id: I4accb0b690173d93ad6f4c9dd0bce66d8de75faa
Reviewed-by: Niels Weber <niels.weber@theqtcompany.com>

src/plugins/qmakeprojectmanager/qmakekitinformation.cpp

@@ -45,7 +45,7 @@ QmakeKitInformation::QmakeKitInformation()
     setPriority(24000);
 }
 
-QVariant QmakeKitInformation::defaultValue(Kit *k) const
+QVariant QmakeKitInformation::defaultValue(const Kit *k) const
 {
     Q_UNUSED(k);
     return QString();