ath9k: avoid usage of ath9k_hw_setpower() on hw.c

ath9k_hw_setpower() is a core driver helper with locking
protection. Locking protection should be left to the driver
core, not the hw code. Hardware code no longer contends for
locking when it needs to wake up the chip or put it to sleep.

Signed-off-by: Luis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>