ath6kl: Fix bug in scheduling hb_timer

hb_timer should be scheduled only when hb_poll is non-zero.
But in ath6kl_recovery_work() the timer is scheduled based
on fw_recovery.enable instead which is wrong.

Signed-off-by: Vasanthakumar Thiagarajan <vthiagar@qca.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>