ath6kl: Fix inactivity timeout for AR6004

Currently AR6004 handles the inactivity timeout resolution
in minutes rather than seconds. So parse the inactivity timeout
to the firmware in minutes. For now we will cleanup the
inactive station entries to the nearest converted minutes
(ex:  an inactive time of 70 seconds would take atleast 2 - 3 minutes)
Tested with surprise removal of client cards/host shutdown.

Cc: Manikandan Radhakrishnan <mradhakr@qca.qualcomm.com>
Reported-by: Leela Kella <leela@qca.qualcomm.com>
Signed-off-by: Mohammed Shafi Shajakhan <mohammed@qca.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>