ath9k: describe hw initialization better

During initialization ath9k tends to use "attach" to when we
initialize hardware due to the fact we used to attach a "HAL".
The notion of a HAL is long gone, so lets just be clear on what
we are doing.

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