qcacmn: Update the mc timer state after its deleted

Currently qdf mc timer stop api updates mc timer state
to QDF_TIMER_STATE_STOPPED before it deletes the timer which
may lead to race condition where if any other thread tries to
read the state of the timer and re-start the timer considering
it is stopped which may get deleted after that.

To address above issue, update the timer state after timer
delete.

Change-Id: I302b89bdedf23f8277eacb6d42b5bd8e6daa4d05
CRs-Fixed: 2643254