USB: replace kernel_thread() with kthread_run() in libusual.c

Replaced kernel_thread() with kthread_run() since kernel_thread() is
deprecated in drivers/modules.

Signed-off-by: Cedric Le Goater <clg@fr.ibm.com>
Cc: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Matthew Dharm <mdharm-usb@one-eyed-alien.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>