ath5k: write PCU registers on initial reset

"Ath5k: unify resets"
introduced a regression into 2.6.28 where the PCU registers are never
initialized, due to ath5k_reset() always passing true for change_channel.
We subsequently program a lot of these registers but several may start
in an unknown state.

Cc: stable@kernel.org
Reported-by: Forrest Zhang <forrest@hifulltech.com>
Signed-off-by: Bob Copeland <me@bobcopeland.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>