cfg80211: use enum nl80211_dfs_regions for dfs_region everywhere

u8 was used in some other places, just stick to the enum,
this forces us to express the values that are expected.

Signed-off-by: Luis R. Rodriguez <mcgrof@do-not-panic.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
diff --git a/net/wireless/nl80211.c b/net/wireless/nl80211.c
index 7b73132..79632ed 100644
--- a/net/wireless/nl80211.c
+++ b/net/wireless/nl80211.c
@@ -5079,7 +5079,7 @@
 	char *alpha2 = NULL;
 	int rem_reg_rules = 0, r = 0;
 	u32 num_rules = 0, rule_idx = 0, size_of_regd;
-	u8 dfs_region = 0;
+	enum nl80211_dfs_regions dfs_region = NL80211_DFS_UNSET;
 	struct ieee80211_regdomain *rd = NULL;
 
 	if (!info->attrs[NL80211_ATTR_REG_ALPHA2])