iwlwifi: dvm: use macros for format strings

Some static checkers (e.g. smatch) complain if a non-constant
format string is used, even if that's a static const variable.
Since there's no impact on code generation, just change those
format strings to be macros.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>