perf script: Fix error when printing 'weight' field

In SPE traces the 'weight' field can't be printed in 'perf script'
because the 'dummy:u' event doesn't have the WEIGHT attribute set.

Use evsel__do_check_stype(..) to check this field, as it's done with
other fields such as "phys_addr".

Before:

  $ perf record -e arm_spe_0// -- sleep 1
  $ perf script -F event,ip,weight
  Samples for 'dummy:u' event do not have WEIGHT attribute set. Cannot print 'weight' field.

After:

  $ perf script -F event,ip,weight
     l1d-access:               12 ffffaf629d4cb320
     tlb-access:               12 ffffaf629d4cb320
         memory:               12 ffffaf629d4cb320

Fixes: b0fde9c6 ("perf arm-spe: Add SPE total latency as PERF_SAMPLE_WEIGHT")
Signed-off-by: German Gomez <german.gomez@arm.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lore.kernel.org/r/20220221171707.62960-1-german.gomez@arm.com


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>