selftests/ftrace: Fix dependencies for some of the synthetic event tests

Commit b81a3a10 ("tracing/histogram: Add simple tests for
stacktrace usage of synthetic events") changed the output text in
tracefs README, but missed updating some of the dependencies specified
in selftests. This causes some of the tests to exit as unsupported.

Fix this by changing the grep pattern. Since we want these tests to work
on older kernels, match only against the common last part of the
pattern.

Link: https://lore.kernel.org/linux-trace-kernel/20230614091046.2178539-1-naveen@kernel.org

Cc: <linux-kselftest@vger.kernel.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>
Fixes: b81a3a10 ("tracing/histogram: Add simple tests for stacktrace usage of synthetic events")
Signed-off-by: Naveen N Rao <naveen@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

tools/testing/selftests/ftrace/test.d/trigger/inter-event/trigger-synthetic-event-dynstring.tc

 #!/bin/sh
 # SPDX-License-Identifier: GPL-2.0
 # description: event trigger - test inter-event histogram trigger trace action with dynamic string param
-# requires: set_event synthetic_events events/sched/sched_process_exec/hist "char name[]' >> synthetic_events":README ping:program
+# requires: set_event synthetic_events events/sched/sched_process_exec/hist "' >> synthetic_events":README ping:program
 
 fail() { #msg
     echo $1

tools/testing/selftests/ftrace/test.d/trigger/inter-event/trigger-synthetic_event_syntax_errors.tc

 #!/bin/sh
 # SPDX-License-Identifier: GPL-2.0
 # description: event trigger - test synthetic_events syntax parser errors
-# requires: synthetic_events error_log "char name[]' >> synthetic_events":README
+# requires: synthetic_events error_log "' >> synthetic_events":README
 
 check_error() { # command-with-error-pos-by-^
     ftrace_errlog_check 'synthetic_events' "$1" 'synthetic_events'