ath9k: Fix RTC_DERIVED_CLK usage

ath9k: Fix RTC_DERIVED_CLK usage

commit 4e6ce4dc7ce71d0886908d55129d5d6482a27ff9 upstream.

Based on the reference clock, which could be 25MHz or 40MHz,
AR_RTC_DERIVED_CLK is programmed differently for AR9340 and AR9550.
But, when a chip reset is done, processing the initvals
sets the register back to the default value.

Fix this by moving the code in ath9k_hw_init_pll() to
ar9003_hw_override_ini(). Also, do this override for AR9531.

js: remove AR_SREV_9531 test as 9531 support is not in 3.12 yet

Signed-off-by: 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>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>