ath9k: Fix QuickDrop usage

Bit 5 in the miscConfiguration field of the base EEPROM
header denotes whether QuickDrop is enabled or not. Fix
the incorrect usage of BIT(1) and also make sure that
this is done only for the required chips.

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