I haven't been able to get hostapd logging to respond to any of the "hooks" involved myself, nor, as I understand, have several others.
From what I gather, you'll need to make sure that the logger you're using for OpenWRT is processing debug-level messages. I personally use syslog-ng so can't confirm that the stock logger will log from hostapd at a debug level.
Within your /etc/config/wireless definition, you'll need to enable debug-level logging. From there the OpenWRT network scripts will extract it to /var/run/hostapd-phy1.conf and put it into "hostapd.conf" lingo.
Some very recent info on trying to remove info-level logging at Advice needed about Wifi Security
I did some checking and posted results on https://bugs.openwrt.org/index.php?do=details&task_id=1468