iwlwifi: mvm: rename scan_calc_params to scan_calc_dwell

To make things clearer, rename the iwl_mvm_scan_calc_params() function
to iwl_mvm_calc_dwell() and make it calculate and fill in only
dwell-related parameters.

Signed-off-by: Luciano Coelho <luciano.coelho@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>