iwlwifi: mvm: small fix in a comment about UMAC scan schedules

The UMAC API supports multiple scan schedules, but now we use only a
single one.  Change the comment to make this clear and avoid
confusion.

Signed-off-by: Luciano Coelho <luciano.coelho@intel.com>
Reviewed-by: David Spinadel <david.spinadel@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>