perf test: Fix exit code for record+probe_libc_inet_pton.sh

perf test: Fix exit code for record+probe_libc_inet_pton.sh

This fixes record+probe_libc_inet_pton.sh from always exiting with code
0 and making the test pass even if the perf script output does not match
the expected pattern.

The issue can be observed if this test is run with the verbose flags as
shown below:

  60: probe libc's inet_pton & backtrace it with ping       :
  ...
  ping 19602 [006] 16988.413767: probe_libc:inet_pton: (7fff9a2c42e8)
  1842e8 __GI___inet_pton (/usr/lib64/libc-2.26.so)
  130db4 getaddrinfo (/usr/lib64/libc-2.26.so)

  FAIL: expected backtrace entry 3 ".*\(.*/bin/ping.*\)$" got ""
  test child finished with 0
  ...
  probe libc's inet_pton & backtrace it with ping: Ok

Signed-off-by: Sandipan Das <sandipan@linux.vnet.ibm.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Fixes: e07d585e2454 ("perf tests: Switch trace+probe_libc_inet_pton to use record")
Link: http://lkml.kernel.org/r/20180312124450.30371-1-sandipan@linux.vnet.ibm.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>