Remove noop check in setSortRole

The noop check m_sortRole == role has to be removed
because the hash table m_roleIds can change between two calls to
setSortRole (as it actually happens when resync the hash table).

Possibly one could perform a more clever check (i.e. adding some
m_invalidated flag which would override the check), but I am not sure it is
really worth it.

This fixes sorting issues in the Plasma Device Notifier

CCMAIL:notmart@gmail.com

declarativeimports/core/datamodel.cpp

@@ -111,9 +111,6 @@ QString SortFilterModel::filterRole() const
 
 void SortFilterModel::setSortRole(const QString &role)
 {
-    if (m_sortRole == role) {
-        return;
-    }
     m_sortRole = role;
     if (role.isEmpty()) {
         sort(-1, Qt::AscendingOrder);