USB: cxacru: Cleanup sysfs attribute code

This changes the format of unknown status values to be less verbose and
uses an array instead of several different snprintf calls. Since only
enum values are assigned to it, poll_state is changed from int to enum.
Use abs() for dB values instead of two almost identical return lines.

Signed-off-by: Simon Arlott <simon@fire.lp0.eu>
Acked-by: Duncan Sands <duncan.sands@math.u-psud.fr>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>