iwlwifi: scan: Modify return value of a function

The function iwl_mvm_umac_scan_fill_6g_chan_list() always returns 0.
Change its return value to 'void'.

Signed-off-by: Ilan Peer <ilan.peer@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Link: https://lore.kernel.org/r/iwlwifi.20220204122220.caef72dc255c.I186b787c7f190ca00c2800e1035f2503360f58a8@changeid


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