ath9k: Unify reset API

Instead of having ath_reset_internal() and ath_reset()
as two separate calls to perform a HW reset, have
one function. This makes sure that the behavior will
be the same at all callsites.

Signed-off-by: Sujith Manoharan <c_manoha@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>