[meshcop] include logging.hpp for helper function 'LogError()' (#5562)

LogError() uses otLogWarnMeshCoP(), which was included by
thread/thread_netif.hpp -> meshcop/joiner.hpp -> common/logging.hpp.
thread_netif.hpp includes joiner.hpp only if OT_JOINER=ON, so the
build would fail if OT_JOINER=OFF.

This commit fixes the above.

src/core/meshcop/meshcop.cpp

@@ -36,6 +36,7 @@
 #include "common/crc16.hpp"
 #include "common/debug.hpp"
 #include "common/locator-getters.hpp"
+#include "common/logging.hpp"
 #include "crypto/pbkdf2_cmac.h"
 #include "crypto/sha256.hpp"
 #include "mac/mac_types.hpp"