iwlwifi: remove AMT check from transport

As iwl_prepare_card_hw() is idempotent (and
many cards support AMT anyway) there's no
point in calling iwl_prepare_card_hw() only
for AMT capable devices -- call it always
and simplify the code that way.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>