tracing histograms: Simplify parse_actions() function

tracing histograms: Simplify parse_actions() function

The parse_actions() function uses 'len = str_has_prefix()' to test which
action is in the string being parsed. But then it goes and repeats the
logic for each different action. This logic can be simplified and
duplicate code can be removed as 'len' contains the length of the found
prefix which should be used for all actions.

Link: https://lore.kernel.org/all/20240107112044.6702cb66@gandalf.local.home/
Link: https://lore.kernel.org/linux-trace-kernel/20240107203258.37e26d2b@gandalf.local.home
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Andy Shevchenko <andy@kernel.org>
Cc: Tom Zanussi <zanussi@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>