Clear current PMKSA cache selection on association/roam

Clear current PMKSA cache selection on association/roam

It was possible for the RSN state machine to maintain old PMKSA cache
selection (sm->cur_pmksa) when roaming to another BSS based on
driver-based roaming indication. This could result in mismatching state
and unexpected behavior, e.g., with not generating a Suite B PMKSA cache
entry.

Signed-off-by: Jouni Malinen <jouni@codeaurora.org>