iwlwifi: mvm: clean up iwl_mvm_bss_info_changed_ap_ibss

Remove the enum abuse (using an enum to store a set of values),
the unneeded ret variable and unnecessary if nesting.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>