tracing: Change `if (strlen(glob))` to `if (glob[0])`

No need to traverse to the end of string. If the first byte is not a NUL
char, it's guaranteed `if (strlen(glob))` is true.

Link: https://lkml.kernel.org/r/20220417185630.199062-3-ammarfaizi2@gnuweeb.org

Cc: Ingo Molnar <mingo@redhat.com>
Cc: GNU/Weeb Mailing List <gwml@vger.gnuweeb.org>
Signed-off-by: Ammar Faizi <ammarfaizi2@gnuweeb.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

kernel/trace/trace_events_hist.c

@@ -6217,7 +6217,7 @@ static int event_hist_trigger_parse(struct event_command *cmd_ops,
 	if (WARN_ON(!glob))
 		return -EINVAL;
 
-	if (strlen(glob)) {
+	if (glob[0]) {
 		hist_err_clear();
 		last_cmd_set(file, param_and_filter);
 	}