HID: fix start/stop cycle in usbhid driver

`stop' left out usbhid->urb* pointers and so the next `start' thought
it needs to allocate nothing and used the memory pointers previously
pointed to. This led to memory corruption and device malfunction.

Also don't forget to clear disconnect flag on start which was left set
by the previous `stop'.

This fixes

	echo DEVICE > /sys/bus/hid/drivers/DRIVER/unbind
	echo DEVICE > /sys/bus/hid/drivers/DRIVER/bind

failures.

Signed-off-by: Jiri Slaby <jirislaby@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>