ath9k: fix misplaced debug code

The commit 'ath9k: Add more information to debugfs xmit file.' added more
debug counters to ath9k and also added some lines of code to ath9k_hw.

Since ath9k_hw is also used by ath9k_htc, its code must not depend on ath9k
data structures. In this case it was not fatal, but it's still wrong, so
the code needs to be moved back to ath9k.

Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Cc: Ben Greear <greearb@candelatech.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>