iwlwifi: provide firmware version

By setting the firmware version in wiphy it is possible to obtain this
information via ethtool. Some examples,

	    # ethtool -i wlan1
	    driver: iwlagn
	    version: 2.6.32-rc5-wl-56840-g26d8540
	    firmware-version: 228.57.2.23
	    bus-info: 0000:03:00.0
	    # ethtool -i wlan0
	    driver: iwl3945
	    version: 2.6.32-rc5-wl-56840-g26d8540
	    firmware-version: 15.28.2.8
	    bus-info: 0000:02:00.0

Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>