sof_perf_analyzer: fix float_format not callable error

[golowanow]

1. Fix float_format string passed to pandas to_csv() and to_html() to be a callable object resolving 'TypeError: 'str' object is not callable' observed (with pandas==2.1.4)

2. Fix missing return statement at skip_to_first_trace() pylint R1710 'inconsistent return statement'.

For 1) - no issue with pandas==1.3.5, but TypeError with pandas==2.1.4+dfsg

Traceback (most recent call last):
  File "/home/ubuntu/sof-test/tools/sof_perf_analyzer.py", line 306, in 
    main()
  File "/home/ubuntu/sof-test/tools/sof_perf_analyzer.py", line 303, in main
    print_perf_info()
  File "/home/ubuntu/sof-test/tools/sof_perf_analyzer.py", line 269, in print_perf_info
    stats.to_html(args.out2html, float_format='%.3f', index=False)
  File "/usr/lib/python3/dist-packages/pandas/core/frame.py", line 3235, in to_html
    return fmt.DataFrameRenderer(formatter).to_html(
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3/dist-packages/pandas/io/formats/format.py", line 1074, in to_html
    string = html_formatter.to_string()
             ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3/dist-packages/pandas/io/formats/html.py", line 88, in to_string
    lines = self.render()
            ^^^^^^^^^^^^^
  File "/usr/lib/python3/dist-packages/pandas/io/formats/html.py", line 94, in render
    self._write_table()
  File "/usr/lib/python3/dist-packages/pandas/io/formats/html.py", line 269, in _write_table
    self._write_body(indent + self.indent_delta)
  File "/usr/lib/python3/dist-packages/pandas/io/formats/html.py", line 417, in _write_body
    fmt_values = self._get_formatted_values()
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3/dist-packages/pandas/io/formats/html.py", line 412, in _get_formatted_values
    fmt_values = {i: self.fmt.format_col(i) for i in range(self.ncols)}
                     ^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3/dist-packages/pandas/io/formats/format.py", line 893, in format_col
    return format_array(
           ^^^^^^^^^^^^^
  File "/usr/lib/python3/dist-packages/pandas/io/formats/format.py", line 1296, in format_array
    return fmt_obj.get_result()
           ^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3/dist-packages/pandas/io/formats/format.py", line 1329, in get_result
    fmt_values = self._format_strings()
                 ^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3/dist-packages/pandas/io/formats/format.py", line 1398, in _format_strings
    fmt_values.append(float_format(v))
                      ^^^^^^^^^^^^^^^
TypeError: 'str' object is not callable

[golowanow]

SOFCI TEST