perf trace: Print the name of a syscall when failing to read its info

perf trace: Print the name of a syscall when failing to read its info

When failing to read the tracepoint event format, like currently with
sys_execve, that is not defined via SYSCALL_DEFINE macros and thus
doesn't have an entry in:

  $ ls -d /sys/kernel/debug/tracing/events/syscalls/sys_enter_*exec*
  /sys/kernel/debug/tracing/events/syscalls/sys_enter_kexec_load
  $

Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Namhyung Kim <namhyung@gmail.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/n/tip-`ranpwd
Link: http://lkml.kernel.org/n/tip-q3ak0j8b81yxylykq5wp2uwi@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>