iwlwifi: Fix -EIO error code that is never returned

Currently the error -EIO is being assinged to variable ret when
the READY_BIT is not set but the function iwlagn_mac_start returns
0 rather than ret. Fix this by returning ret instead of 0.

Addresses-Coverity: ("Unused value")
Fixes: 7335613a ("iwlwifi: move all mac80211 related functions to one place")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Link: https://lore.kernel.org/r/20210907104658.14706-1-colin.king@canonical.comSigned-off-by: Luca Coelho <luciano.coelho@intel.com>

drivers/net/wireless/intel/iwlwifi/dvm/mac80211.c

@@ -299,7 +299,7 @@ static int iwlagn_mac_start(struct ieee80211_hw *hw)
 
 	priv->is_open = 1;
 	IWL_DEBUG_MAC80211(priv, "leave\n");
-	return 0;
+	return ret;
 }
 
 static void iwlagn_mac_stop(struct ieee80211_hw *hw)