Ignore the error when the perf probe failed to find inline function
instances. This can happen when we search a method in C++ debuginfo.  If
there is completely no instance in target, perf probe can return an
error.

E.g. without this fix:
  ----
  $ perf probe -x /usr/lib64/libstdc++.so.6 -vD showmanyc
  probe-definition(0): showmanyc
  symbol:showmanyc file:(null) line:0 offset:0 return:0 lazy:(null)
  0 arguments
  symbol:catch file:(null) line:0 offset:0 return:0 lazy:(null)
  symbol:throw file:(null) line:0 offset:0 return:0 lazy:(null)
  symbol:rethrow file:(null) line:0 offset:0 return:0 lazy:(null)
  Open Debuginfo file: /usr/lib/debug/usr/lib64/libstdc++.so.6.0.22.debug
  Try to find probe point from debuginfo.
  Matched function: showmanyc
  An error occurred in debuginfo analysis (-2).
  Trying to use symbols.
  Failed to find symbol showmanyc in /usr/lib64/libstdc++.so.6.0.22
    Error: Failed to add events. Reason: No such file or directory (Code: -2)
  ----

This is because one of showmanyc is defined as inline but no instance
found. With this fix, it is succeeded to show as below.
  ----
  $ perf probe -x /usr/lib64/libstdc++.so.6 -D showmanyc
  p:probe_libstdc++/showmanyc /usr/lib64/libstdc++.so.6.0.22:0xb0e50
  p:probe_libstdc++/showmanyc_1 /usr/lib64/libstdc++.so.6.0.22:0xc7c40
  p:probe_libstdc++/showmanyc_2 /usr/lib64/libstdc++.so.6.0.22:0xecfa0
  p:probe_libstdc++/showmanyc_3 /usr/lib64/libstdc++.so.6.0.22:0x115fc0
  p:probe_libstdc++/showmanyc_4 /usr/lib64/libstdc++.so.6.0.22:0x121a90
  ----
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Tested-by: Jiri Olsa <jolsa@kernel.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/147464489775.29804.3190419491209875936.stgit@devboxSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>