ath9k: Fix thermometer programming

The registers that control the on-chip thermometer
need to be programmed based on the chainmask that
the solution supports, not the chainmask that is
present in the eeprom.

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