iwl3945: remove bogus comment

I added this comment myself, but it's clearly wrong. I had meant
to place it in iwl_mac_add_interface, which at the time didn't
honour the MAC address setting, but it does now.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>