ath: fix DFS timestamp wraparound reset condition

The DFS pattern detector ought to reset the
detector lines when a pulse is added with
lower time stamp than the previous (which
indicates a TSF restart).

This did not work so far and is fixed with
this patch.

The modification does not change detection
performance within the driver, since it
only ensures early reset (which is later
performed by the PRI detectors anyway).
It is relevant for synthetic tests and
statistical evaluations, where millions
of pulse patterns are processed and an
early reset helps reducing load.

Signed-off-by: Zefir Kurtisi <zefir.kurtisi@neratec.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>