Update usb_timings_sysctl_handler() to accept any value for timings between
0 milliseconds and 2 seconds inclusivly. Some style fixes while at it.

The USB specification has minimum values and maximum values,
and not only minimum values.

Sponsored by: Mellanox Technologies // NVIDIA Networking

(cherry picked from commit 00e501d720d46386e6c8d0ebb4b3a8e98cb0390e)