Remove exra whitespace from files (#189)

* Remove multiple newlines at the end of files
* Remove the whitespace from the end of lines

wireless/ieee802154/mac802154_ioctl.c

@@ -164,4 +164,3 @@ int mac802154_ioctl(MACHANDLE mac, int cmd, unsigned long arg)
     }
   return ret;
 }
-

wireless/ieee802154/mac802154_purge.c

@@ -82,4 +82,3 @@ int mac802154_req_purge(MACHANDLE mac, uint8_t msdu_handle)
 #endif
   return -ENOTTY;
 }
-

wireless/ieee802154/mac802154_sync.c

@@ -77,4 +77,3 @@ int mac802154_req_sync(MACHANDLE mac, FAR struct ieee802154_sync_req_s *req)
 #endif
   return -ENOTTY;
 }
-