iwlwifi: cause build error on missing newline

If a (debug) message is missing a newline, cause build error
so we don't keep reintroducing this problem.

This also prevents using a non-constant argument as the format
string which is a good idea anyway (e.g. for security reasons.)

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>