udc_stop() should clear ->driver pointer unconditionally to let the UDC
framework to work correctly with both registering/unregistering gadgets
and enabling/disabling gadgets by writing to
/sys/class/udc/*hsotg/soft_connect interface.
Acked-by: NPaul Zimmerman <paulz@synopsys.com>
Signed-off-by: NMarek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: NFelipe Balbi <balbi@ti.com>