WUSB: correct format of wusb_chid sysfs file

Make the wusb_chid sysfs file match the ABI documentation.

Print all zeros if the WUSB host is stopped (instead of an empty file)
and end the file with a newline.

Signed-off-by: David Vrabel <david.vrabel@csr.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>