ath9k: Fix temperature compensation

The registers for temperature compensation need to
be programmed only for active chains. Use the TX chainmask
to make sure that this is done properly for QCA953x.

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