iwlwifi: update comments on the debug interface

Bring up-to-date some comments on the location of debug files.

Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
Acked-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Zhu Yi <yi.zhu@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>