iwlwifi: fix 40MHz operation setting on cards that do not allow it

Some devices have 40MHz operation disabled entirely. Ensure that driver do
not enable 40MHz operation if a channel does not allow this.

This fixes http://bugzilla.intellinuxwireless.org/show_bug.cgi?id=2135

Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
CC: stable@kernel.org
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/iwlwifi/iwl-eeprom.c

@@ -749,7 +749,8 @@ static int iwl_mod_ht40_chan_info(struct iwl_priv *priv,
 	ch_info->ht40_eeprom = *eeprom_ch;
 	ch_info->ht40_max_power_avg = eeprom_ch->max_power_avg;
 	ch_info->ht40_flags = eeprom_ch->flags;
-	ch_info->ht40_extension_channel &= ~clear_ht40_extension_channel;
+	if (eeprom_ch->flags & EEPROM_CHANNEL_VALID)
+		ch_info->ht40_extension_channel &= ~clear_ht40_extension_channel;
 
 	return 0;
 }