iwlwlifi: update rx write pointer w/o request mac access in the CAM mode

In iwl_rx_queue_update_write_ptr function
replace iwl_write_direct32 with iwl_write32 when not in power save mode.
We don't have to go through grab nic access as the NIC is already awake.

Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>