ath9k: Reduce deep indentation

The EDMA case is handled first, so the else condition
can be removed.

Signed-off-by: Sujith Manoharan <c_manoha@qca.qualcomm.com>
Acked-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>