tracing: Check that the synthetic event and field names are legal

Call the is_good_name() function used by probe events to make sure
synthetic event and field names don't contain illegal characters and
cause unexpected parsing of synthetic event commands.

Link: https://lkml.kernel.org/r/c4d4bb59d3ac39bcbd70fba0cf837d6b1cedb015.1602598160.git.zanussi@kernel.org

Fixes: 4b147936

 (tracing: Add support for 'synthetic' events)
Reported-by: Masami Hiramatsu <mhiramat@kernel.org>
Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org>
Tested-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Tom Zanussi <zanussi@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>