perf expr: Return -EINVAL for syntax error in expr__find_ids()

perf expr: Return -EINVAL for syntax error in expr__find_ids()

expr__find_ids() propagates the parser return value directly.  For syntax
errors, the parser can return a positive value, but callers treat it as
success, e.g., for below case on Arm64 platform:

  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

Convert positive parser returns in expr__find_ids() to -EINVAL, as a
result, the error value will be respected by callers.

Before:

  perf stat -C 5
  Failure to read '#slots'Failure to read '#slots'Failure to read '#slots'Failure to read '#slots'Segmentation fault

After:

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

Fixes: ded80bda8bc9 ("perf expr: Migrate expr ids table to a hashmap")
Signed-off-by: Leo Yan <leo.yan@arm.com>
Reviewed-by: Ian Rogers <irogers@google.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>