zd1201: replace function ieee80211_{dsss_chan_to_freq, freq_to_dsss_chan}

Replace ieee80211_{dsss_chan_to_freq, freq_to_dsss_chan} with more
generic ieee80211_{channel_to_frequency, frequency_to_channel}.

Function ieee80211_frequency_to_channel() will return 0 if frequency
is not correctly provided, so no need to set channel to 0 explicitly.

Include <net/cfg80211.h> for the defination of IEEE80211_BAND_2GHZ.
Because <net/cfg80211.h> includes <linux/ieee80211.h>, so we can
replace <linux/ieee80211.h> with <net/cfg80211.h>.

This change is a preparation for the removal of function
ieee80211_{dsss_chan_to_freq, freq_to_dsss_chan}.
Signed-off-by: Zhao, Gang <gamerh2o@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/zd1201.c

@@ -18,7 +18,7 @@
 #include <linux/netdevice.h>
 #include <linux/etherdevice.h>
 #include <linux/wireless.h>
-#include <linux/ieee80211.h>
+#include <net/cfg80211.h>
 #include <net/iw_handler.h>
 #include <linux/string.h>
 #include <linux/if_arp.h>
@@ -914,11 +914,8 @@ static int zd1201_set_freq(struct net_device *dev,
 
 	if (freq->e == 0)
 		channel = freq->m;
-	else {
-		channel = ieee80211_freq_to_dsss_chan(freq->m);
-		if (channel < 0)
-			channel = 0;
-	}
+	else
+		channel = ieee80211_frequency_to_channel(freq->m);
 
 	err = zd1201_setconfig16(zd, ZD1201_RID_CNFOWNCHANNEL, channel);
 	if (err)