USB: s3c2410: unregister should call unbind, not disconnect

This patch (as1275) fixes the s3c2410 device controller driver.  Its
usb_gadget_unregister_driver() routine is supposed to call the gadget
driver's unbind method, not the disconnect method.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>