iwlwifi: dvm: use %u for sscanf() into unsigned variable

Use %u instead of using %d which looks signed but then won't
get signed output if using an unsigned variable. It doesn't
matter much, but be consistent.

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