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