ath6kl: don't power down hardware when interface is down

Jouni reported that my patch "ath6kl: power down hardware when interface
is down" caused a regression on his x86 boxes and scan didn't work anymore.
I was able to reproduce the problem by disabling all debug messages.

So there has to be a race condition somewhere in the code and disable the
functionality until the race is fixed. Now hardware is powered from the
point where module is loaded until it's removed.

Reported-by: Jouni Malinen <jouni@qca.qualcomm.com>
Tested-by: Jouni Malinen <jouni@qca.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>