ath6kl: small cleanup in ath6kl_htc_pipe_rx_complete()

It's harmless, but Smatch complains if we use "htc_hdr->eid" before
doing the bounds check.

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