FCMTokenRestHandler: fix reporting fcm service name
FCMTokenRestHandler: fix reporting fcm service name

The PrintHandler::value() method does not overload input argument
const char *. Values of const char * are converted to int and not
to std::string.

Fixes: 383699f36810 ("FCMTokenRestHandler: list available notification services")
Signed-off-by: Jan Viktorin <3eab6ac54c005c4408f608556a6663b7f2abede7@fit.vutbr.cz>

BeeeOn/server,BeeeOn/server,BeeeOn/server,BeeeOn/server