tracing: Have existing event_command.parse() implementations use helpers

Simplify the existing event_command.parse() implementations by having
them make use of the helper functions previously introduced.

Link: https://lkml.kernel.org/r/b353e3427a81f9d3adafd98fd7d73e78a8209f43.1644010576.git.zanussi@kernel.org



Signed-off-by: Tom Zanussi <zanussi@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>