tracing: Use match_string() instead of open coding it in trace_set_options()

tracing: Use match_string() instead of open coding it in trace_set_options()

match_string() returns the index of an array for a matching string,
which can be used to simplify the code.

Link: http://lkml.kernel.org/r/[email protected]
Reviewed-by: Andy Shevchenko <[email protected]>
Signed-off-by: Yisheng Xie <[email protected]>
Signed-off-by: Steven Rostedt (VMware) <[email protected]>