ath9k_hw: fix analog shift register writes on AR9003

Writes to the analog shift registers, which are issues by the initval
programming function, require a 100 usec delay (similar to AR9002,
but in a different register range).

Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Acked-by: Luis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>