ath9k: Fix bugs in programming registers during PA CAL

* First PA driver (PDPADRV1) was not powered down properly.
* Compensation capacitor for dynamic PA was programmed incorrectly.

Also, remove a stray REG_READ.

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