ath9k: Fix ANI trigger threshold

Since raising/lowering the limits based on INI has
been changed, the error limit for OFDM has to be 1000,
not 3500.

Signed-off-by: Sujith Manoharan <c_manoha@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>