iwlagn: fix compilation when debug flags is unset

Trivial fixes to allow compilation without warnings when debug
compilation flag isn't set.
Also fix the compilation when debugfs flag isn't set.
Fix a warning: unused priv pointer on the way.

Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>