iwlwifi: fix compile warning

The patch fixes compile warning for ‘iwl4965_hw_channel_switch’ defined
but not used.
Signed-off-by: NZhu Yi <yi.zhu@intel.com>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>

drivers/net/wireless/iwlwifi/iwl-4965.c

@@ -1607,6 +1607,7 @@ static int iwl4965_send_rxon_assoc(struct iwl_priv *priv)
 	return ret;
 }
 
+#ifdef IEEE80211_CONF_CHANNEL_SWITCH
 static int iwl4965_hw_channel_switch(struct iwl_priv *priv, u16 channel)
 {
 	int rc;
@@ -1647,6 +1648,7 @@ static int iwl4965_hw_channel_switch(struct iwl_priv *priv, u16 channel)
 	rc = iwl_send_cmd_pdu(priv, REPLY_CHANNEL_SWITCH, sizeof(cmd), &cmd);
 	return rc;
 }
+#endif
 
 static int iwl4965_shared_mem_rx_idx(struct iwl_priv *priv)
 {