tracing: Convert function graph set_flags() to use a switch() statement

tracing: Convert function graph set_flags() to use a switch() statement

Currently the set_flags() of the function graph tracer has a bunch of:

  if (bit == FLAG1) {
	[..]
  }

  if (bit == FLAG2) {
	[..]
  }

To clean it up a bit, convert it over to a switch statement.

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: https://patch.msgid.link/20251114192319.117123664@kernel.org
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>