ath9k_hw: fix hardware deinit

Without this you will get a panic if the device initialization
fails. Also, free ath_hw instance properly. ath9k_hw_deinit()
shouldn't do it.

Cc: stable@kernel.org
Signed-off-by: Sujith <Sujith.Manoharan@atheros.com>
Signed-off-by: Luis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>