wifi: iwlwifi: mvm: avoid iterating over an un-initialized list

The initiator smooth list is initialized only in iwl_mvm_up(), but is
cleared in iwl_mvm_mac_stop. This may result in iterating over the
list before it was initialized in case iwl_mvm_up() failed early.
Fix it by moving the list initialization to an earlier stage.

Fixes: b68bd2e3

 ("iwlwifi: mvm: Add FTM initiator RTT smoothing logic")
Signed-off-by: Avraham Stern <avraham.stern@intel.com>
Signed-off-by: Gregory Greenman <gregory.greenman@intel.com>
Link: https://lore.kernel.org/r/20230416154301.b50b1fe9a576.Ie348ffae110612d2e252ac120a3ba0aea063b1b6@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>