pm-graph: sleepgraph: Avoid crashing on binary data in device names

A regression has occurred in the hid-sensor code where a device
name string has not been initialized to 0, and ends up without
a NULL char and is printed with %s. This includes random binary
data in the device name, which makes its way into the ftrace output
and ends up crashing sleepgraph because it expects the ftrace output
to be ASCII only.

For example: "HID-SENSOR-INT-020b?.39.auto" ends up in ftrace instead
of "HID-SENSOR-INT-020b.39.auto". It causes this crash in sleepgraph:

  File "/usr/bin/sleepgraph", line 5579, in executeSuspend
    for line in fp:
  File "/usr/lib/python3.10/codecs.py", line 322, in decode
    (result, consumed) = self._buffer_decode(data, self.errors, final)
UnicodeDecodeError: 'utf-8' codec can't decode byte 0xff in position
1568: invalid start byte

The issue is present in 6.3-rc1 and is described in full here:
https://bugzilla.kernel.org/show_bug.cgi?id=217169

A separate fix has been submitted to have th...