iwlwifi: mvm: add fall through comments where needed

Some switch-cases were missing a fall through comment, so the compiler
may warn.  Fix that by adding the comments where needed.  In other
cases there was more text in the comment, which the compiler doesn't
recognize, so either remove the extra text or move it to a separate
comment line as appropriate.

Signed-off-by: Luca Coelho <luciano.coelho@intel.com>