carl9170 firmware: fix CAB MAC RESET regression

commit "carl9170 firmware: improve tx ampdu ba_end handling"
introduced a serious regression.

Since the wlan_trigger was missing, the flushed CAB frames
were stuck in tx queue. This of course lead to countless
warnings from the tx watchdog as it reseted the MAC
processor over and over again.

Signed-off-by: Christian Lamparter <chunkeey@googlemail.com>