ath9k_htc: Fix sparse endian warnings

This patch fixes a bunch of endian issues that
were exposed by sparse. It's a miracle that the driver
worked at all till now.

The Lord be praised.

Signed-off-by: Sujith <Sujith.Manoharan@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>