ath6kl: Fix htc_packet leak in ath6kl_htc_rx_process_packets()

Packet is not reclaimed when ath6kl_htc_rx_process_hdr() fails.
Fix this by deferring the packet deletion from comp_pktq till
ath6kl_htc_rx_process_hdr() returns success. This bug is found
in code review, impact is not easily visible as the leak happens
only in failure cases.

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