psm(4): Always initialize used values in debug print

'status' array passed to get_mouse_status() is usually uninitialized by
callers.

Fully populating it with values in get_mouse_status() can fail due to
read_aux_data().

Additionally, nothing in API constrains 'len' to be >= 3. In practice,
every caller passes three, so perhaps that argument should just be removed.
Refactoring is a larger change, though.

Remove use of potentially uninitialized values by:

1. Only printing 3 debug statuses if the passed array was at least 'len' >= 3;
2. Populating 'status' array up to first three elements, if read_aux_data() failed.

No functional change intended.

Reported by: Coverity
Sponsored by: Dell EMC Isilon