regulatory: use IS_ERR macro family for freq_reg_info

Instead of returning an error and filling a pointer
return the pointer and an ERR_PTR value in error cases.

Acked-by: Luis R. Rodriguez <mcgrof@do-not-panic.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
diff --git a/include/net/cfg80211.h b/include/net/cfg80211.h
index f3be58a..1f74360 100644
--- a/include/net/cfg80211.h
+++ b/include/net/cfg80211.h
@@ -2938,22 +2938,22 @@
  * freq_reg_info - get regulatory information for the given frequency
  * @wiphy: the wiphy for which we want to process this rule for
  * @center_freq: Frequency in KHz for which we want regulatory information for
- * @reg_rule: the regulatory rule which we have for this frequency
  *
  * Use this function to get the regulatory rule for a specific frequency on
  * a given wireless device. If the device has a specific regulatory domain
  * it wants to follow we respect that unless a country IE has been received
  * and processed already.
  *
- * Returns 0 if it was able to find a valid regulatory rule which does
- * apply to the given center_freq otherwise it returns non-zero. It will
- * also return -ERANGE if we determine the given center_freq does not even have
- * a regulatory rule for a frequency range in the center_freq's band. See
- * freq_in_rule_band() for our current definition of a band -- this is purely
- * subjective and right now its 802.11 specific.
+ * When an error occurs, for example if no rule can be found, the return value
+ * is encoded using ERR_PTR(). Use IS_ERR() to check and PTR_ERR() to obtain
+ * the numeric return value. The numeric return value will be -ERANGE if we
+ * determine the given center_freq does not even have a regulatory rule for a
+ * frequency range in the center_freq's band. See freq_in_rule_band() for our
+ * current definition of a band -- this is purely subjective and right now it's
+ * 802.11 specific.
  */
-extern int freq_reg_info(struct wiphy *wiphy, u32 center_freq,
-			 const struct ieee80211_reg_rule **reg_rule);
+const struct ieee80211_reg_rule *freq_reg_info(struct wiphy *wiphy,
+					       u32 center_freq);
 
 /*
  * callbacks for asynchronous cfg80211 methods, notification