perf metricgroup: Refine error logs

perf metricgroup: Refine error logs

Return -ENOENT when no metric/group matches, and directly use the return
value from expr__find_ids(), so -EINVAL is reserved for parse failures.

Print separate logs to make it clear.

Before:

  perf stat -C 5 -vvv
  Using CPUID 0x00000000410fd490
  metric expr 100 * (STALL_SLOT_BACKEND / (CPU_CYCLES * #slots) - BR_MIS_PRED * 3 / CPU_CYCLES) for backend_bound
  parsing metric: 100 * (STALL_SLOT_BACKEND / (CPU_CYCLES * #slots) - BR_MIS_PRED * 3 / CPU_CYCLES)
  Failure to read '#slots'
  literal: #slots = nan
  syntax error
  Cannot find metric or group `Default'

After:

  perf stat -C 5 -vvv
  Using CPUID 0x00000000410fd490
  metric expr 100 * (STALL_SLOT_BACKEND / (CPU_CYCLES * #slots) - BR_MIS_PRED * 3 / CPU_CYCLES) for backend_bound
  parsing metric: 100 * (STALL_SLOT_BACKEND / (CPU_CYCLES * #slots) - BR_MIS_PRED * 3 / CPU_CYCLES)
  Failure to read '#slots'
  literal: #slots = nan
  syntax error
  Fail to parse 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>