ath6kl: remove false check from ath6kl_rx()

Dan found a check from ath6kl_rx() which doesn't make any sense at all:

"  1327          if (status || !(skb->data + HTC_HDR_LENGTH)) {
                                ^^^^^^^^^^^^^^^^^^^^^^^^^^
skb->data is a pointer.  This pointer math is always going to be false.
Should it be testing "packet->act_len < HTC_HDR_LENGTH" or something?"

I don't know what the check really was supposed to do, but I think Dan's guess
is right. Fix it accordingly.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>