iwlwifi: update testmode command of direct register access

In order to make sure the testcommand function of direct register
access can be performed even NIC is asleep, replace corresponding
handler iwl_read32 and iwl_write32 by using iwl_direct_read32 and
iwl_direct_write32.

Signed-off-by: Kenny Hsu <kenny.hsu@intel.com>
Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>