[radio] unify around otExtAddress type (#2029)

src/cli/cli.cpp

@@ -881,7 +881,7 @@ void Interpreter::ProcessExtAddress(int argc, char *argv[])
 
     if (argc == 0)
     {
-        otBufferPtr extAddress(otLinkGetExtendedAddress(mInstance));
+        otBufferPtr extAddress(reinterpret_cast<const uint8_t *>(otLinkGetExtendedAddress(mInstance)));
         OutputBytes(extAddress, OT_EXT_ADDRESS_SIZE);
         mServer->OutputFormat("\r\n");
     }