perf trace: Fix an exit code of trace__symbols_init

perf trace: Fix an exit code of trace__symbols_init

Currently if trace_event__register_resolver() fails, we return -errno,
but we can't be sure that errno isn't zero in this case.

Signed-off-by: Andrei Vagin <avagin@openvz.org>
Reviewed-by: Jiri Olsa <jolsa@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Vasily Averin <vvs@virtuozzo.com>
Link: http://lkml.kernel.org/r/20171108002246.8924-2-avagin@openvz.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>