USB: usbcore get rid of the timer in usb_start_wait_urb()
This patch uses completion timeout instead of a timer to implement
a timeout when submitting an URB in usb_start_wait_urb().
It also fixes a small issue. With the previous code, if no timeout
happened and the URB's status was set to ECONNRESET value, the code
assumed wrongly that a timeout had occured.