Correct the actual definition of ath_tx_tid_filt_comp_single() to
match how it's used.

This is another bug that led to aggregate traffic hanging because
the BAW tracking stopped being accurate. In this instance, a filtered
frame that exceeded retries would return a non-error, which would
mean the caller would never remove it from the BAW. But it wouldn't
be added to the filtered list, so it would be lost forever. There'd
thus be a hole in the BAW that would never get transmitted and
this leads to a traffic hang.

Tested:

• Routerstation Pro, AR9220 AP