wifi: cfg80211: debugfs: fix return type in ht40allow_map_read()

The return type is supposed to be ssize_t, which is signed long,
but "r" was declared as unsigned int.  This means that on 64 bit systems
we return positive values instead of negative error codes.

Fixes: 80a3511d ("cfg80211: add debugfs HT40 allow map")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Link: https://lore.kernel.org/r/YutvOQeJm0UjLhwU@kiliSigned-off-by: Johannes Berg <johannes.berg@intel.com>

net/wireless/debugfs.c

@@ -65,9 +65,10 @@ static ssize_t ht40allow_map_read(struct file *file,
 {
 	struct wiphy *wiphy = file->private_data;
 	char *buf;
-	unsigned int offset = 0, buf_size = PAGE_SIZE, i, r;
+	unsigned int offset = 0, buf_size = PAGE_SIZE, i;
 	enum nl80211_band band;
 	struct ieee80211_supported_band *sband;
+	ssize_t r;
 
 	buf = kzalloc(buf_size, GFP_KERNEL);
 	if (!buf)