usb: gadget: pch_udc: Fix disconnect issue

usb: gadget: pch_udc: Fix disconnect issue

BugLink: http://bugs.launchpad.net/bugs/987337

commit c50a3bff0edb0acd49d8033a12ea4668e09a31ad upstream.

ISSUE:
When the driver notifies a gadget of a disconnect event, a system
rarely freezes.

CAUSE:
When the driver calls dev->driver->disconnect(), it is not calling
spin_unlock().

Signed-off-by: Tomoya MORINAGA <tomoya.rohm@gmail.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>