ath6kl: Avoid processing failed rx packets

It is not necessary to process an htc_packet which is allocated for rx
but failed in sdio rx. Though it does not fix any real issue, it does
not make much sense to process the failed frame.

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