ath9k: call ath9k_hw_detach() once upon hw init failure

If hw initialization fails (ath9k_hw_init()) on ath_init_softc()
we bail out and call ath9k_hw_detach(). The call ath9k_hw_detach()
is conditional though as ath9k_hw_init() could itself have called
ath9k_hw_detach(). Just describing this is itself a brain twister.
Avoid this nonsense by removing ath9k_hw_detach() from ath9k_hw_init().

Upon hw initialization failure we expect the callers to take care of
the cleanup.

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