wlcore: Fix memory leak in wlcore_cmd_wait_for_event_or_timeout

In case memory resources for *events_vector* were allocated, release
them before return.

Addresses-Coverity-ID: 1470194 ("Resource leak")
Fixes: 4ec7cece ("wlcore: Add missing PM call for wlcore_cmd_wait_for_event_or_timeout()")
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>