ath9k: fix missed error codes in the tx status check

My previous change added in:

 commit 815833e7
    ath9k: fix tx status reporting

was not checking all possible tx error conditions. This could possibly
lead to throughput issues due to slow rate control adaption or missed
retransmissions of failed A-MPDU frames.

This patch adds a mask for all possible error conditions and uses it
in the xmit ok check.

Cc: stable@kernel.org
Reported-by: Björn Smedman <bjorn.smedman@venatech.se>
Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>