perf scripts python: exported-sql-viewer.py: Fix warning display

perf scripts python: exported-sql-viewer.py: Fix warning display

Deprecation warnings are useful only for the developer, not an end user.
Display warnings only when requested using the python -W option. This
stops the display of warnings like:

 tools/perf/scripts/python/exported-sql-viewer.py:5102: DeprecationWarning:
         an integer is required (got type PySide2.QtCore.Qt.AlignmentFlag).
         Implicit conversion to integers using __int__ is deprecated, and
         may be removed in a future version of Python.
    err = app.exec_()

Since the warning can be fixed only in PySide2, we must wait for it to
be finally fixed there.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: stable@vger.kernel.org      # v5.3+
Link: http://lore.kernel.org/lkml/20210521092053.25683-4-adrian.hunter@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>