iwlwifi: mvm: fix and improve printing of rate scale table

Info about VHT/HT rates wasn't printed properly when dumping
the rate scale table. Fix that and print more info. While at it
fix some other minor issues in the printing and prevent
overflowing the print buffer.

Signed-off-by: Eyal Shapira <eyal@wizery.com>
Reviewed-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>