ieee80211: Fix dissect_hs20_osu_provider() return parameter

With the current return parameter of dissect_hs20_osu_provider() function, the dissector only show the first
osu_provider of the list. Changing the return end by return offset, the
dissector show all osu_provider of the list.

epan/dissectors/packet-ieee80211.c

@@ -8432,7 +8432,7 @@ dissect_hs20_osu_provider(proto_tree *tree, tvbuff_t *tvb,
     proto_item_set_len(pi, offset - start_offset);
   }
 
-  return end;
+  return offset;
 }
 
 static void