perf trace: Fix exclusion of not available syscall names from selector list

perf trace: Fix exclusion of not available syscall names from selector list

We were just skipping the syscalls not available in a particular
architecture without reflecting this in the number of entries in the
ev_qualifier_ids.nr variable, fix it.

This was done with the most minimalistic way, reusing the index variable
'i', a followup patch will further clean this by making 'i' renamed to
'nr_used' and using 'nr_allocated' in a few more places.

Reported-by: Leo Yan <leo.yan@linaro.org>
Tested-by: Leo Yan <leo.yan@linaro.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
Cc: Mike Leach <mike.leach@linaro.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
Fixes: 04c41bcb862b ("perf trace: Skip unknown syscalls when expanding strace like syscall groups")
Link: https://lkml.kernel.org/r/20190613181514.GC1402@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>