ath5k: improve comments for optimized tx descriptor setup

Comment the use of local variables to reduce the number of load/store
operations on uncached memory, in hopes of not losing this optimization
accidentally in the future.

Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
1 file changed