ath9k: Add a delay between RTC reset/clear for AR9003

The small delay that is present between a RTC reset/clear
operation is required for the chip to settle and this is
needed for all chips, not just the AR9002 family.

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