ath9k: Fix return code when ath9k_hw_setpower() fails on reset

We were not reporting a status code back ath9k_hw_setpower() failed
during reset so lets correct this.

Reported-by: Jiri Slaby <jirislaby@gmail.com>
Signed-off-by: Luis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: David S. Miller <davem@davemloft.net>