usb: roles: Take care of driver module reference counting

This fixes potential "BUG: unable to handle kernel paging
request at ..." from happening.

Fixes: fde0aa6c

 ("usb: common: Small class for USB role switches")
Cc: <stable@vger.kernel.org>
Acked-by: Hans de Goede <hdegoede@redhat.com>
Tested-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>