perf expr: Add '\n' in literal parse errors

perf expr: Add '\n' in literal parse errors

Add a trailing newline for logs.

Before:

  perf stat -C 5
  Failure to read '#slots'Cannot find metric or group `Default'

After:

  perf stat -C 5
  Failure to read '#slots'
  Cannot find metric or group `Default'

Signed-off-by: Leo Yan <leo.yan@arm.com>
Reviewed-by: Ian Rogers <irogers@google.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>