perf buildid-list: Fix return value of perf buildid-list -k

The buildid string length is returned by perf buildid-list -k command.
Since a non-zero return value means an error, perf buildid-list -k cmd
should return 0 when successful instead.

Before:

	# perf buildid-list -k
	39356d74e96e02346fe0ec1f3f162b6c522bac62
	# echo $?
	41

After:

	# perf buildid-list -k
	39356d74e96e02346fe0ec1f3f162b6c522bac62
	# echo $?
	0

Signed-off-by: Michael Petlan <mpetlan@redhat.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Fixes: 0b5a7935 ("perf buildid: Introduce sysfs/filename__sprintf_build_id")
LPU-Reference: 1449080871.24573.145.camel@redhat.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>